Parkers overall rating: 4.6 out of 5 4.6

The best time to buy a convertible is…?

Richard Kilpatrick is running an approved-used Mercedes-Benz C-Class Cabriolet as it approaches three years old - and the end of its warranty

Buying a convertible car in winter - Mercedes C 250 d Cabriolet

Just as the price of 4x4s rises and supply dwindles in winter, the determination of used-car dealers to sell any convertibles they have in stock must surely rise – and we’ve found it to be true, the best time of year to buy a convertible is between November and April. This applies particularly to the cheaper end of the market, where a £2,000 Volvo C70 or Mercedes-Benz SLK may fall to three figures when the frost forms on the windscreen.

The actual saving available on newer, more expensive cars is worth more in cash terms though. We’ve chosen a March 2017 registered approved-used Mercedes-Benz C 250 d Cabriolet as our latest used long-term test car (previously we’ve run a Mercedes-Benz S-Class and a Volvo V40).

It’s a spec that would have the widest appeal – Selenite Grey, with the 204hp 2.1-litre diesel and desirable Premium Plus pack; it’s also got attractive 19-inch multispoke alloys; new, it was over £46,000.

Mercedes-Benz C-Class AMG 19-inch multispoke alloy wheel

As a four-seater convertible, it’s one of the smaller options now available – though still a bit bigger than a typical family hatchback. Other options include the Audi A5 Cabriolet, the BMW 4 Series Convertible, and at a push, the Vauxhall Cascada. Don't laugh - the Vauxhall's affordable, well engineered and a popular used larger cabriolet albeit one that lacks the premium feel and badge prestige of the C-Class and its main rivals, and it occupies the space once owned by the Saab 9-3 Convertible as much as the Astra.

Want to read more about our used C 250 d Cabriolet? Scroll down, or click the links to read the most recent/relevant update.

Nice car – how much did it cost?

At two and a half years old, with 15,300 miles on the clock, it’s had a gentle life but is approaching the end of the original warranty and support period; the retail price of £25,192 is, for many used buyers, a significant chunk of cash.

Mercedes’ own finance offering on a £25,300 C 250 d Cabriolet works out – roughly – at £387 per month over 48 months, with a deposit of £4,426 and an optional final payment of £9,675. The APR, of 12.9%, means you’re paying around £7,000 in interest – you may be able to find your own finance for considerably less.

2017 Mercedes-Benz C 250 d Cabriolet in Selenite Grey, Premium Plus with 19-inch wheels

A quick check of comparison sites suggests that if you’ve got the deposit and an excellent credit rating, you can finance the balance at 5.9% APR over 48 months for £470 per month - without a balloon payment at the end. With finance-backed cash, you may be able to get a better deal, and there’s no risk of extra charges if you exceed the mileage limits.

If you think that’s costing as much per month as a new one – think again. Leasing offers on a comparable C 220 d AMG Line Premium Plus come in at £4,699 initial payment and £674 per month for 48 months for the same 10,000 miles per year basis.

There’s another rival when you’re looking at spending this much, and it’s likely to be sat right next to the C-Class you’re looking at. Scaled up, the E-Class Cabriolet from 2017-on has a more refined 2.0-litre diesel, a more practical boot and more rear legroom – despite being a class above, the difference in price for comparable spec can be as little as £2,000, making a used E 220 d Cabriolet something of a bargain in our opinion. You’ll need to look for a December 2017-on C-Class to get the same engine and infotainment technology…

Why a C-Class, then?

Living in a city, the C-Class feels usefully smaller – narrower – than the E-Class; on paper the difference is just 49mm, but the cosier interior design contributes to the perception that this is a sportier car. The difference in length is more obvious, as the C 250 d needs 160mm less to find a space. At 4,686mm long, it’s about the same size as a Skoda Octavia or Ford Focus Estate.

2017 C-Class Cabrolet roof down, Selenite Grey C 250 d

It’s also styled to look like a scaled-down S-Class Cabriolet, rather than a C-Class with the roof removed, and looks brilliant with the roof down. At least until you deploy the AirCap system, when it gains the quirky-looking windscreen spoiler and pop-up wind deflector at the rear. Effective as AirCap is, it doesn’t do anything for the pose-factor…

The choice of engine is more pragmatic, as this car comes from the era of diesels being everywhere and yet, the combination of diesel plus convertible seems odd. We’ve gone for the more powerful C 250 d, which has the same 2.1-litre engine as the contemporary C 220 d but with 204hp instead of 170hp. It will reach 62mph in 7.2 seconds and allegedly do 151mph, justifying the ‘roadster’ badge on the front.

Having said that, even the C-Class saloon only comes in Sports or AMG type trims in the UK, meaning a flat bonnet badge and a large grille star, rather than the upright three-pointed star mascot and more relaxed, mature aura of more conservative Mercedes models.

Boot space is adequate rather than generous, particularly with the roof down – the E-Class is much better in this regard – and rear space is compromised for longer trips or taller occupants, but still reasonable for most adults.

First impressions – Mercedes Approved-Used

As an approved used car that’s less than three years old, it’s effectively gained a few months of warranty and breakdown assistance – though Mercedes are very good at providing aftersales backup for as long as the car has been serviced by an approved dealer. With services competitively priced, and relatively far apart (around 15,000 miles in this case), that’s not an unreasonable burden.

All the existing infotainment services last until the car’s three years old – which includes map updates, Mercedes-Me functions like GeoFencing and tracking, and included subscriptions.

More recent cars, with more sophisticated versions of Mercedes Comand Online benefit more – this one offers just a few features. Older cars (from 2002-onwards) can get a few of these features too, with a free (at the time of writing) adapter from Mercedes.

Mercedes-Me mobile app and car display

The C 250 d was delivered spotlessly clean, serviced and with a full tank of fuel and I’d assumed, AdBlue. Just a small mark on the offside rear alloy was noted, though I found a small scratch on the inside of the fuel filler later on; it’s hard to believe the car’s two and a half years old. The steering wheel is a little shinier than a showroom-fresh one, but you'd only know if you compared directly.

A205 W205 C-Class AdBlue Cannot Measure Fluid Level warning

It may have been sitting for a while before arriving here, as on the drive home the AdBlue system reported a fault – 'cannot measure fluid level'. Topping it up confirmed my suspicions – it was already full. The nearest dealer to work, Mercedes-Benz of Peterborough, attended to the problem at the earliest opportunity first thing on a Monday morning, taking a little over an hour.

The AdBlue was fine, but the level sensors needed recalibrating; there’s been no recurrence - so far...

Mercedes-Benz W205/A205 C-Class AdBlue warning 500 miles

Although a warning saying you won’t be able to start the car in 500 miles is rather worrying, the speed with which it was resolved is reassuring; we didn’t buy the car from them, I’m not an existing customer, and they treated it with the same urgency as I’d expect had we just driven away from their showroom in it.

And buying in winter?

There’s a definite sense of delayed gratification – the roof’s been down to take the pictures when Mercedes delivered the car, and since then it’s been cold, wet and determinedly autumnal. On the other hand, the C-Class is a refined, warm cabriolet with excellent heated seats, effective air conditioning and secure rear-wheel drive handling. With temperatures now reaching freezing, the sports tyres have so far proven secure, and the iced-up car defrosts very rapidly despite the diesel engine and traditional blower, rather than heated screen tech. Downside is that it has the kind of windows that drop when you open the door, and I've never been fond of those in icy conditions. Remote start would help a lot here.

You can get a 4Matic all-wheel drive model, but they’re relatively scarce, meaning discounts are unlikely.

Nice weather to buy a convertible?

Personally, I’m used to this – I’ve owned convertible cars since passing my test, and had no qualms about driving with the roof down on crisp winter days. With less expensive models (okay, let’s just say bangers) like old MX-5s, Saabs or Rover 200s, it’s just what the cars are. However… With a car at this price, you might be better off saving for a few months longer and buying in March-April.

First 1,000 miles report

AdBlue reset aside, so far, so good. For many used car buyers, that first 1,000 miles is when you'll find faults and risk the first pangs of buyers' remorse; the C-Class is actually going in the other direction as I get used to a low-slung sporty car in place of a high-riding, soft pickup truck.

Everything works perfectly, and the Mercedes has been subjected to some pretty vile rain and cold already. Driving in Birmingham, the car feels a good fit – not too big for narrow, double-parked streets – though the ride from the AMG Line suspension and 19-inch wheels can be a little unforgiving on more neglected roads, the seats compensate somewhat.

It’s returning 43mpg on average, though with Eco mode and low-congestion routes that’s approached 50mpg. I'm looking forward to a long drive and some interesting destinations over the next six months.

C-Class Cabriolet: 2018 C 250 d Selenite Grey, rear, roof up

Update 2: Performance, ride and handling

In 2017, this was the third-least powerful option you could choose for your C-Class Cabriolet, above the C 220 d 170hp diesel and C 200 184hp petrol. As always, power is only half the story - the C 250 d's 500Nm at 1,600rpm is remarkably close to the Mercedes-AMG C 43's 520Nm at 2,000 rpm, so it's a very worthy rival to the C 300.

Not that it feels that potent in normal driving.

Making use of the 2.1-litre diesel's torque for relaxed progress, the C-Class doesn't come across as swift or eager as the numbers suggest, and the standard chassis doesn't encourage driving like a hooligan even with the optional 19-inch alloy wheels. Remote and relatively heavy at speed, the otherwise precise steering gives little feedback, yet you can feel road imperfections through the seat as a constant, small shuffle.

Bigger ripples, ridges and variations in road surface keep the body moving - though if you do get an newly-surfaced stretch of motorway it's impressively smooth; somewhat surprisingly, it's rare that the car is caught out by big thuds in town (I slow down for speedbumps though, as I doubt it'll float over them at 30mph like a Qashqai or Volvo S90).

On stretches of neglected fast road, though, you soon learn to pay extra attention to the tarmac for the high-speed holes that pepper the interminable M6 roadworks, as it sounds painful if you catch one. So far, though, any such incidents have been all noise - the wheels and tyres are fine.

Mercedes-Benz C 250 d Cabriolet, 2017, Selenite Grey at Waddesdon Manor, sunset

I suspect that refinement suffers for Mercedes' insistence that UK buyers don't want the comfort suspension, perhaps - even the entry-level Sport is 15mm lower than a regular C-Class - but maybe they're right. It's always composed and generally rides very well for a sporty convertible on big wheels. It would be more in character if it were softer, though, and there is a way to get that.

We know that the Airmatic suspension transforms even the smallest Mercedes cabriolet into a genuinely serene cruiser; it's just usually paired with the least serene AMG engines. Find a four-cylinder model that got it as an option, and you'll have a very chilled-out cabriolet.

There's not much scuttle shake (flex from the lack of a roof, most often felt as the dashboard wobbling out of time with the seats over ruts and bumps), either, and the only trim rattle so far has been an easily silenced chittering from the instrument surround on cold mornings - perhaps the plastic shrinks very slightly. Consider it a traditional Mercedes trait, as my 500 SL and A 170 CDI did exactly the same thing in the same conditions!

So, C-Class or E-Class for drivers?

Compared to an E-Class Cabriolet, the smaller C feels very at home on British country roads, and displays the same determined competence when tackling smooth curves and fast corners as it does when keeping straight ahead on the motorway. It corners with only moderate lean, and grips well in the dry - in the wet, the combination of wide, low-profile front tyres, rear-wheel drive and an understeer-biased setup (aided by staggered wheels that are narrower on the front than the rear) is safe rather than exciting.

Mercedes-Benz C 250 d Cabriolet, 2017, Selenite Grey at Waddesdon Manor, sunset

There's really no appreciable wear in the bushes, suspension or brakes at this age - everything works entirely as designed without rattling or softness, and my own experence of secondhand Mercedes suggests that should remain the case for another 40,000 miles or so. My '98 SLK was still on the same dampers 17 years later and though new ones made a big difference to refinement and how it felt putting power down out of bends, it never felt dangerous or worn - just less solid.

You can't fault the way the car moves when driven enthusiastically, either - that diesel might not be the last word in refinement (it can be heard idling from 30ft away quite clearly) but it has the torque to pull away from persistent tailgaters, complete overtaking briskly and pick up pace rapidly on more enjoyable A-roads. Like many aspects of this Cabriolet, there's little emotional stimulation or excitement - it's just incredibly good at its job.

I expect the Mercedes-AMG C 43 Cabriolet, with that characterful V6 turbo's bark and confidence-inspiring 4Matic all-wheel-drive, is an absolute blast though. Like the C 250 d's wayward twin that went backpacking in Berlin and spent a summer in Ibiza instead of going to the London School of Economics.

Kicking the tyres on our C-Class

A normal C 250 d Sport would have 17-inch wheels, and an AMG Line, 18-inch - the big multi-spoke alloys are quite an upgrade, visually and in terms of the impact they have on ride and handling. AMG Line cars also get sportier drilled brake discs.

Mercedes-Benz AMG 19-inch multi-spoke titanium alloy, 2017 C-Class

Looking at the options list, this £595 extra should also include run-flat tyres, which would normally remove the Tirefit kit. There's definitely a can of goop and a compressor in the boot, though (normal spec on a 2017 AMG Line Premium Plus with standard wheels), so what's the story? Time to have look.

First of all, the Mercedes C-Class that shows on Mercedes-Me has the correct wheels, so it was almost certainly built with them - they're not a later addition. Have the tyres been changed? A powerful, rear-wheel drive car can get through a set of rear tyres in 10,000 miles easily.

As an approved-used Mercedes, this car's wheels would be inspected before sale - and so, we find tyres that match, and have plenty of tread on them. As the staggered setup means replacement would cost from £600 to £800 for a full set with decent brands, it's something to consider when comparing used cars outside the dealer network.

That saving on advertised price might have a few thousand just waiting to surprise you in hidden costs, or it might be an opportunity to save even more by knowing how the car should be presented, and immediately getting four correct tyres, instead of accepting fresh tread on inferior ones fitted by a used-car dealer cutting costs.

Mercedes C-Class Cabriolet Tirefit kit

It's wearing Dunlop SportMaxx RTs. Not only are these run-flats - though the marketing and sidewalls don't shout this fact - they're a Mercedes-approved model (the internet's full of opinions about this, but the upshot is they're a couple of pounds more than non-MO variants). So far they've proved admirably grippy for a summer tyre despite temperatures dropping below seven degrees, and everything I'd heard about runflats and road noise must be out of date, as they don't seem any worse than other low-profile tyres of this size.

I've always gone with Continental or Avon on my rear-wheel drive Mercedes cars in the past, and Michelin Energy on my A-Classes, so this is a new experience for me; I haven't felt any difference in day-to-day driving so far and overall, am very impressed with the cold weather grip and poise in corners.

You can get budget tyres for these very low-profile sizes (255/35 on the rear) but... why? There's not much point in a lifetime guarantee on an unknown brand if you've just sabotaged the bit that keeps you on the road for the sake of £60/corner. As the front and rear wheels can't be rotated, don't forget to check any used example you're considering for mismatched brands or uneven wear.

Although there's a little slip and aquaplaning in heavy rain, the C 250 d's able to get out of tricky right-hand junctions swiftly and securely, and that's about the only time it's asked to put that 500Nm through the back wheels with any aggression. As winter takes hold, though, we'll see how the summer tyres cope - or get a sent of winter boots.

Update 3: Comfort in context

Perhaps as a consequence of Mercedes-Benz's commitment to rear-wheel drive, perhaps because the firm now offers something like thirty different styles of car, the C-Class Cabriolet is, rationally, a very odd mix of things.

Every time I drive, I'm trying to suss out what sort of car this is, who it's for - even comparing it to the four-seater convertibles I've owned before. It seems that I may be the worst person in the world to judge this, because I'm entirely happy driving really old (in the worn-out, not prized-classic sense) cars and would drive a 1994 Ford Escort Cabriolet if that was all I could get without a roof.

This is a £46,000 premium model styled to look like a miniature version of a £100,000 status symbol, rather than a relatively compact family car with no roof - yet as a two year old used car, it's surprisingly affordable.

Think Blackadder handing Baldrick an iPad to work out their next cunning plan, and you've got an idea of just how much of a culture shock the C-Class is to my cabriolet consciousness. I mean, the last car I bought was a £350 Rover 214 Cabriolet. A soft-top for posers, it was not. Nor was it particularly pleasant to drive. Or cosseting. Or reliable...

Rover 214 Cabriolet - once, a respectable four-seater convertible

But it was surprisingly pleasant for four adults to enjoy the sun in, once the 1980s-style suspension, gearbox and brakes were allowed for.

So everyone is telling me that the C-Class Cabriolet is, primarily, a car of compromises designed for the driver to look good in and tell the world how awesome their lifestyle is. All I can tell you is that while I really like it from the driver's seat, it's often tripped over by the engineering choices if you're expecting practicality - and if you don't need practicality, why not show off your freedom with two seats and a V8?

Motorway magnificence and urban ease

Supportive, ergonomic seats are bread-and-butter for Mercedes - this level of C-Class has electric adjustment including thigh support, and although the bolsters are more on the sports than gentle side of grippy, there's plenty of width for broad shoulders. Electric steering wheel adjustment, and three memories, make it easy to set up for different drivers - or 'that stage on the commute where you want to shift position but wouldn't normally move seats around'.

Despite the rather over-the-top 19-inch wheels and low-profile runflat tyres, the C 250 d has a relaxed, gentle loping pace on the motorway that's rarely interrupted by minor imperfections, and it's very comfortable for long drives - as long as you're okay with the low roofline.

Ferocious heating and airscarf add to the luxurious feel, but only newer and more expensive models get massaging features. Given that this used C-Class cost less than a new, well-equipped Skoda Scala, I'll forgive it for being so inattentive.

One aspect of comfort that can get overlooked in reviews is the visibility. For the most part, the C-Class Cabriolet is good - it's got a fairly generous glass rear window, and the dashboard, wheel and windscreen combine with good sightlines. However, the LED headlights have an abrupt transition from bright, consistent lighting to dark contrast when dipped. If you can, seek out the more sophisticated adaptive LEDs if you drive a lot at night. I'm still not convinced that the alignment is right, but I'm assured it is - and comparing beam distance with other cars on the motorway it doesn't look wildly short, just very sudden in how it cuts off.

Footwell space is adequate, rather than generous, and I suspect a manual would almost be cramped for such a wide car overall. It does have plenty of places to rest your arms, including the massive centre console box and crucially for a convertible, a low enough window sill to get one tanned arm. The cabin is compact, though, and you can even reach back to the rear seat cupholders from the front seat. This is a four seater on paper, but if that's your main concern you might want to look elsewhere.

Mercedes-Benz C-Class cabin, rear seats

When the C-Class arrived, I tried the back seat out for space - with the driver's seat on my settings, I can sit behind it just fine. My head almost touches the roof lining, but there's room to get feet under the seat, and only the very upright seat back makes it uncomfortable for more than half an hour or so.

However, filling those rear seats with two teenage kids - albeit one who is rapidly approaching 6ft - results in a barrage of complaints that are frustrating because 'when I was growing up' I'd frequently get stuffed into the back of cars like a Mk 1 Golf Cabriolet or travel with friends sardined into 1980s Ford Fiestas.

On the other hand, maybe because my parents had owned open-topped cars before, I know I wanted to travel in the open air - and what compromises that entails. If you don't actually want the roof down, the comfort-focused 21st-century kids have a point - the rear seat backs are quite sharply upright, the legroom can be minimal if the driver and front passenger want the bulky electric seats moved back for even average height.

5' 10" passenger behind driving position for 5' 10" driver - rear view from the C-Class Cabriolet

This is a trait partly shared with the C-Class Coupe. I'm well shy of 6ft tall, but sitting in the back of the fixed-roof model the low roofline and rear pillar leave a mere sliver of light at chest height, as you stare at the headlining rather than at the scenery. The Cabriolet's view out with the roof up is slightly better than the Coupe, and the view with it down is excellent.

Do child seats fit the C-Class Cabriolet?

Absolutely. The fixed two-seat bench in the back is wide enough for modern, high-protection childseats and there are Isofix points - you could easily get two in side-by-side if you needed to. The upright seat backs don't force the booster forward too much, and the biggest drawback is one shared with any larger two-door car - it's a bit awkward getting into the back, and having enough room to open the doors fully is a rare treat in typical car parks. You'll be fine in the parent and child spaces, though.

Childseat in Mercedes C-Class Cabriolet

If you've got younger children, there's a little bit of space for smaller legs - but there's not a huge amount of knee room with the front seat in an average-height driver's position. I've seen worse small hatchbacks; you shouldn't immediately think that starting a family means waving goodbye to your C-Class Cabriolet - though the extra paraphenalia of babies will rapidly eat into the bootspace if you don't have a spare rear seat to carry mats, bags and toys.

Stowing a modern multi-function buggy is another matter..

Try the buggy in the C-Class boot width-wise?

Try the other way - buggy into the boot length-wise, C-Class Cabriolet

What about putting the buggy in the C-Class small wheels first?

Perhaps this wasn't the best choice of buggy after all. The Joie Chrome DLX Travel System (which includes a carry cot, not shown but it would fit into the boot comfortably even with the roof comparment in place) is absolutely brilliant, with precise, gentle steering, an impressive turning circle and smooth, well-damped suspension - but small, it is not.

It is the sort of baby transport system I'd expect a C-Class owner to want, though. So how can we solve this?

Problem solved - put the buggy in the rear passenger seat!

Okay - so this isn't the best solution, but in reality there are plenty of smaller, more efficiently packaged pushchairs - and the restriction isn't the size of the boot itself, but the shape of the opening.

Or you could get a GLC.

Taller families need the E-Class. And that's okay.

So as I've said before - for families, a used E-Class Cabriolet isn't much more expensive, and makes considerably more sense. The C-Class seats are usable by shorter adults and younger kids, but not by fully-grown people who don't want to make allowances for the experience of going in the car.

There's a lot more to this than just leg/knee and headroom though; the two-door C-Classes seem particularly claustrophobic for rear passengers, and that's disappointing. The height of the seat base, the low rear window and roofline is just too close. There's even an area of padding on the roof lining, such is the proximity of your head to the side window frame. The footwell space, often the first concern, is actually pretty generous.

2019 C 220 d rear seats

To help get a handle on these cars, I tend to identify them with now-classic models I used to aspire to. The C-Class is pretty easy - the Coupe is a Ford Capri (from gritty base-spec, to glorious RS3100, with added FF all-wheel drive prototype), the Cabriolet is the version Ford never made, and for sensible people, the saloon and estate are the Cortina. Easy.

Even the E-Class gets to be a Granada and Granada Coupe - go on, picture an E-Class Coupe in metallic brown with a swaggering '70s detective at the wheel...

But the Capri was always usable as a family car. I'm not sure this Mercedes is given humanity's current trend to get taller with each generation.

Are convertibles becoming less relevant?

Feedback and research suggests the the answer to 'what's the C-Class Cabriolet for?' lies in the desire for an upmarket, attractive car and the perception that a Cabriolet is even more of a luxury item.

From that context the C-Class does make a lot of sense - it's luxurious and well-made, but still a lot easier to live with than a larger, more overtly upmarket model. It's still a mixed-message, though - is it opulent, sporty? I can't help but wonder if those needs would be better served buy a C-Class Coupe with a panoramic sunroof. Or even a GLC Coupe.

I've even heard that some people feel unsafe in a convertible not because of the 'safety' of the car - which is not in question, unlike older convertibles - but because being exposed to other people causes anxiety. The idea that you could be attacked for being in the open in your car is quite worrying - has society really reached that state?

This is a convertible that might cause you to worry about safety - Triumph Vitesse

Here's a four-seater convertible you might feel less than safe in...

Either way, as a purely luxury item, living up to that scaled-down S-Class Cabriolet feel - get the adaptive suspension rather than standard springs. If you're prepared to spend this much to feel pampered and decadent in your otherwise everyday-use car, spend a bit more for a petrol one with air suspension - a much, much more luxurious package that completes the pampering of the front two passengers.

Understanding what the C-Class Cabriolet is really for has helped become more comfortable with it, though. I've switched lenses, from 'affordable premium four-seater cabriolet' to 'luxury car that fits cities', and it's making a lot more sense; now to pay more attention to how others are reacting to it.

Update 4: So, how reliable is a three year old C-Class diesel?

'My' C-Class is at an age where British buyers love the feeling of saving on depreciation while still having a car that still looks fresh and new (yes, if it were mine it would have my private plate on). Ultimately it's a car still on sale for about £47,000 new, that cost £25,000.

Almost everything on the C-Class has been brilliant as it clocks over 20,000 miles and approaches that first MOT. It's immensely satsifying as a daily driver, small enough for busy cities but comfortable given the sporty suspension and 19-inch wheels.

I've acclimatised to the engine's torque and the levels of grip available, so the commute's tedium can be lightened with occasional twisty-road enjoyment, too.

Mercedes C 250d Cabriolet roof down, February, on road

Ideally there should be no difference in the day-to-day experience of a new or three-year-old used C-Class for a couple more years. Just - at worst - a few bills for consumables like tyres and brake pads, and those are avoided a little by going for the approved-used model rather than, say, a £21,000 example from a non-Mercedes cut-price dealer.

If you've read from the start, though, you know this C-Class had an early teething issue with the AdBlue system.

The original warranty expires in March 2020; the approved-used 12-month cover would expire in October 2020. If you've just taken on £25,000-worth of car - or debt to use/own that car - that's not many months of reassurance before any faults could be a very expensive experience, so I decided to make sure the Cabriolet's in the best health - and has had all the attention it can - before the warranty runs out.

That was supposed to take the form of a visit to the dealer 'when convenient' to get the maps updated and car checked and MOT tested, but the check engine light returned at the end of 2019, followed by the AdBlue warning. The anxiety-inducing 500 mile countdown expedited the planned visit.

This is a Mercedes-Benz press car - but I'm treating it like it's my own

This is all about the real experience, so Mercedes UK has not been contacted about any issues - when things go wrong, I'm bothering our local dealer in Peterborough as if it's my own car, which gives a more realistic view. I'm an absolute nightmare of a customer, too; I want service without delays, don't really compromise, and get pretty strident if I'm unhappy. The sort of customer who gets the whole subframe replaced on a car, at the garage's expense, when a tyre-fitting place manages to crossthread and break a captive nut for example.

That doesn't mean being impolite, and the dealer had already said they'd do the nav upgrade for me when I had time to leave the car there. It's free during the warranty period and as it still had 2017 maps, was long overdue. Most approved-used sales will include updating the maps and software, but it's worth checking it's been done if that matters to you.

C 250 d AdBlue faults - hardware, or diagnostics?

Thanks to the reappearance of the no-start countdown, the C-Class was booked in via email for the first working day of 2020, rather than waiting for a convenient spot for the updates. That dastardly AdBlue system is a necessary evil if we want clean air, but it's gone from the usual griping about filling your car with noxious synthetic wee, to genuinely wishing it just wasn't part of the equation.

At the start of 2020 - almost 3,000 miles and two months after the car arrived and the AdBlue system failed - it repeated the error. When last reset and filled it had 2900 miles of the magical fluid, it reported 1,300 miles left 3,000 miles later - so something didn't add up.

Or subtract, in this case.

As well as resetting the system again Mercedes-Benz of Peterborough ordered a new AdBlue tank 'just in case', and advised me to come back if the light came back on. Which it did on the drive home - though, thankfully, without the countdown.

On the upside, the 2019 maps now understand the A14/M6 interchange properly.

With no warning messages, just the check engine light showing, the car went straight to the dealer after work, no calling or heads up, to make sure it was okay to drive. It was, but better yet, the AdBlue tank had arrived - and they booked it in right away for a full day in the workshop.

Mercedes C 250 d 2017 AdBlue tank new and used

Resetting the code (something related to NOx sensors, apparently) sent the warning light away for the remaining time until the next visit. After a day in the workshop, and a brand new AdBlue tank, I thought that would be the end of it.

Sadly, no. A month later, February arrives, the remaining AdBlue reaches 1100 miles and instead of showing 1/2 a tank on the AdBlue display and asking for a topup... yes. You've guessed it. Level cannot be measured, and the dreaded countdown.

It's done 20,000 miles - and the AdBlue error has returned despite a new tank being installed

At least this time the mileage seems to make sense - the amount of AdBlue consumed tallies with the distance driven. Thinking that it might just be a glitch, I emptied the remains of the awkward square bottle into the tank, probably about two litres. Even so, the countdown remained - next stop, a proper AdBlue filler like lorries use.

This is a grim looking thing - AdBlue pump at Rothwell Services, Kettering

This is not the sort of environment a posh little convertible should be in. This C-Class has wandered onto the wrong side of the tracks (or at least, the HGV side of the filling station). Overlooked by the 44-tonne titans of the A14, it prepares to down a few shots of the mysterious liquid so potent it can dissolve exhaust fumes...

A pathetic attempt to consume AdBlue like the big trucks do

Do you get points for trying? 1.8 litres is barely a sneeze from the HGV AdBlue pump...

I'd expected it would take about six to eight litres - Mercedes don't actually make it clear if the tank is 8.5 litres or 22-litres in the handbook, after all. The tank was definitely full - it wasn't the pump being odd - so the apparent absence of AdBlue equated to half a tank when the error appeared.

Is the AdBlue system is haunted? In the absence of a priest, I've settled for booking it back in with the dealer - where this time, it's had the new tank drained and refilled with fresh AdBlue. Well, not completely full - the dealer claims you can overfill the tank, and Mercedes' official fill level on Xentry (the dealer diagnostic system) is about 7/8ths full.

As that shows as 7/8s on the dash display, and I can't see how you can 'overfill' the AdBlue tank, I'm still not convinced that 'filling the tank' is a cause of problems in reality - it's definitely not a factor in the faults showing, as I've only added fluid after several hundred miles and the appearance of an error.

This is the fifth visit to the dealer now since the car arrived at the very end of October. It's exceeding one a month, and everthing has related to the AdBlue system.

October - car showed AdBlue issue on drive home from delivery. AdBlue reset while I waited.
December - car showed AdBlue issue on drive back from Scotland - system reset. New AdBlue tank back-ordered. Maps updated.
January - car showed NOx sensor issue - reset while I waited. AdBlue tank had arrived, so booked in to fit
January - day in workshop for new AdBlue tank to be fitted.
February - inability to see AdBlue level returns. Upstream and downstream NOx sensors replaced with updated components, recoded.

21,600 miles, February 17th

Half a tank of AdBlue remaining on the C250d Cabriolet

This might not look that important, but it's the first time since October that the C-Class has reached 1/2 tank of AdBlue and displayed the level, rather than throwing an error code. I think Mercedes-Benz of Peterborough have solved it!

Main dealer support - worth the cost?

In terms of inconvenience, Mercedes-Benz of Peterborough has done absolutely everything to minimise that - offering a loan car without my asking, offering lifts to and from the office, and checking everything that's been queried on the car. They even provided the pictures you see here of the replacement parts fitted.

This isn't really a surprise to me, though it's absolutely worthy of comment - in 25 years of Mercedes ownership, I've always found the dealers to be astonishingly helpful and friendly, even with much older, less valuable cars.

It's not really the 'main dealer' part of it that's the extra expense. I've owned brand-new cars from Fiat, Peugeot, Citroen, Mazda and others, and have found the dealer labour rates and attitudes very variable - you'd think I'd wandered in with a rusty old Ford spraypainted with obscenties, the way the Volkswagen treated me and my brand-new Beetle Cabriolet when it developed a footwell-filling leak. Mercedes dealers have tolerated me looking like a grunge-festival reject and still treated me as well as an S-Class owner; that impression is hard to shake.

It's not even about 'paying for the service' - most of the time I work on my own cars and have just been getting bits from the service desk while, frankly, annoying the sales staff by wasting time dreaming about cars I couldn't afford. I've also found Mercedes genuine parts (consumables and mechanical, anyway) to be very competitively priced, readily available and often discounted for loyal customers.

Service items may be affordable, but subsystems, electronics and modules are different matter. Things like seat adjustment switch packs, ECUs and control panels can get very, very expensive. On a modern car with a lot of these advanced components, I wouldn't want to gamble on them not going wrong as the car ages. You can plan all sorts of contingencies - but there's a good reason why leasing a brand new car of any make can sometimes work out cheaper than financing a three- to seven-year-old example.

Having saved £20,000 or so on the list price, or theoretically up to £300/month on the leasing price, is it possible to spend some money to mitigate risk?

Mercedes-Benz extended warranties - the options

Normally as an approved-used Mercedes-Benz, this car would have a 12-month warranty from the date of purchase, extending mine to October 2020. Whether new or used, though, there's the option to buy a manufacturer extended warranty before the original expires. In this case, Mercedes will usually contact owners to offer cover, but I called in advanced to get some numbers.

Like many aftermarket warranties, the Mercedes-Benz extended warranty is perhaps more accurately described as 'mechanical breakdown insurance'; it's intended to be as comprehensive as the factory one for the most part - but it does not include wear and tear components. Remarkably, until recently a Mercedes extended warranty did cover this - a sign, perhaps, of the commoditisation of Germany's most stoic and rock-solid marque, a firm that once offered a limited 30 year warranty on cars.

Mercedes C 250 d Cabriolet profile, just washed

There's just one level of cover - all factory fitted components, zero excess to pay in the event of a claim. You can pick it up when the approved-used warranty expires, it's not tied into the manufacturer warranty, but these prices apply for a car which has had continuous cover - buying cover after a break would not be so affordable.

For the C 250 d Cabriolet, the cover costs £449 for a year, with two years available for £850. It can also be bought on a rolling monthly basis, at £43/month. If there's been a break in your warranty cover, that price can rise by 30-40%, but otherwise any increase in premium is in line with inflation and insurance premium tax. Cars can be covered up to nine years old, or 120,000 miles.

Don't get too excited by that price if you've got a bigger Mercedes - the C-Class is fortunate enough to fall into the smaller, simpler category for cover (making the premium for the Cabriolet something of a bargain, as the complex roof mechanism and sophisticated seats are covered too - result!). S-Class models are into four figures per year, and Mercedes-AMG models are considerably more - meaning cover for a C 43 4Matic would run to £1699 per year, typically.

For £43 per month, though, it's hard to complain. This AdBlue tank issue and NOx sensors would have cost more than four years cover alone...

What if the Mercedes didn't have a warranty?

Out of warranty, the AdBlue tank would cost around £850, plus a few hours to exhange, install and recalibrate - call it £1500 all-in, thereabouts. The NOx sensors are 'roughly £350 each' and with labour and diagnostics, you're probably looking at another a four-figure bill.

So far, we're at £2,500 (of Mercedes' warranty repairs) to solve the issue of the AdBlue warning coming on, and the map update's worth a couple of hundred out of warranty too

How's that £3K cheaper C-Class from a non-approved dealer, with just legally-required trading standards cover looking now?

If you're buying an out of warranty C-Class from a trader and a similar fault surfaces, be aware that they may well fit secondhand items to reduce their costs and meet their trading standards obligations with no real view to the long-term. How do I know? Well... I worked with the lower-end of secondhand car sales. The margins are tight, the reliability of cars is unpredictable, and it's a real balancing act making money and delivering good service.

It's unlikely that your used car dealer is trying to pull a fast one on you - but as a customer, you may get better value by shopping further up the food chain, particularly for complex or premium cars.

Breakers - assuming they have the right part, as C-Class AdBlue tanks can range from 8.5 litres to 25 litres apparently - will charge £200-300 for a secondhand component. At the very cheapest, you'd probably get back on the road with secondhand bits, with a Mercedes specialist running third-party diagnostic kit for around £500 - and little guarantee that it wouldn't return a few months later.

You can get compatible NOx sensors and hacks for the ECU - which may 'make the problem go away', but mean the car is no longer approved for on-road use and is likely to fail emissions testing.

It's not just a case of unbolting and swapping a part, either. Like so many modern cars, replacement of most emissions-related components would also need time on the diagnostic computer to calibrate and test. As cars like the C-Class become seven-year-old affordable used cars, or 12-year-old bangers, this technology is more of a concern.

A good reason, then, to consider an aftermarket warranty on all but the cheapest, most disposable examples; if nothing else, it means an expert gets paid for the technical bits as well as the nuts and bolts a skilled DIY mechanic can handle.

How's the approved-used experience working out?

Buying approved-used you should have the same high-quality experience as a new car customer if something goes wrong, particularly with cars from Mercedes. If you haven't, I'd like to know about it, and at the very least you can report your experiences in our owners reviews. Much of my experience with used (and new) cars is that 'things are rarely perfect' - and a lot of what shapes how I feel as a driver, and a customer, of a given brand is down to how the dealer handles it when these increasingly complex machines go wrong.

Even the roof cover on the C-Class Cabriolet is complicated - it's got speakers too

Even something as 'simple' as the cover for folded roof is a complex bit of machinery I'd be wary of letting an untrained - or uncaring - mechanic loose on. It includes hydraulics, control cables and even the rear deck speakers.

This is 'my' thirteenth used Mercedes-Benz; the oldest have been early 1980s models, and the most complex, a 1993 500 SEC that I was very much out of my depth with when electrical issues flared up. I wouldn't have been able to get a warranty on that car, but for the parts I could buy Mercedes were very helpful. On the other hand, outside of Mercedes, I've bought nearly-new cars and younger used cars with warranties, and have had wildly different experiences - often, the hardest bit has been persuading the dealership that something that has gone wrong is their problem.

This, above anything else, is where Mercedes has impressed - and for all the reductions in cover on the extended warranty, and the subjective shift in quality and consistency of the cars themselves compared to those 1980s 'hewn-from-granite' legends, the service remains customer-focused to a very high standard.

While I think that these problems are quite likely to surface on any 2015-on C-Class diesel, I don't think I'd be having the same experience if this were a £22,000 C 250 d Cabriolet from a car supermarket.

Update 5: (Ain't no) Sunshine when you're gone

The AdBlue problem is solved!

The last visit to the garage - see above - fixed the AdBlue problems, so I felt confident in finally sharing my C-Class with the rest of the Parkers team. Tom Goodlad took it for a long weekend, and seemed pretty impressed, Tom Wiltshire did the same, and shared my disappointment with the terrible headlight aim (it can't be right, no matter what the dealer's saying) and finally Keith Jones spent most of a week with it - the same week that all the storms receded and finally, the longer days and warming weather offered some top-down opportunities.

Which of course, Keith made the most of on some winding rural Lincolnshire roads...

At least until one of Britain's famous potholes made an appearance, and swerving to avoid it revealed an even worse one hiding inside a puddle. The end result? A flat 19-inch runflat tyre and one cracked AMG alloy wheel...

Pothole-damaged wheel - Mercedes C-Class Cabriolet with 19-inch AMG wheels and runflat tyres

Sorry. TWO flat tyres - the back one's going to follow where the front went after all! Apparently the car drove safely at low speeds for another mile or so to find a safe location to stop, and there's no sign of that damaging the rear wheel - so runflats do seem to have some benefit.

Mercedes Me app showing loss of tyre pressure - two flat tyres

This deflating experience involved recovery back to the dealer on a Sunday afternoon, and a four-figure bill, which with any luck Lincolnshire Council will be picking up in due course.

C250d Cabriolet on flatbed recovery truck, two flat tyres, Mercedes Assist

Swift repairs mean the car was back on the road the next day - surprising, given the non-standard wheels - and it feels okay bar a hint of extra vibration and a distant noise, both of which could be hallucinations as I'm looking for faults. What's impressive is that the steering wheel is dead straight, the car's tracking well, and we can now measure the tyre wear! The new one on the offside front has about 7.5mm, and the nearside has 5mm, and it's the same at the back.

That's not bad going for a car of this weight and performance after 8,000 miles - suggesting the tyres do wear quite evenly, and you can expect around 16,000 miles before thinking about replacement.

As the tyres aren't directional (handed) - just asymmetrical (there's an outside edge when fitting), it might seem odd that the tyres weren't rotated to have the same tread depth on the same axle. Like many rear-wheel-drive Mercedes, the C-Class has staggered wheels that are wider at the back - perhaps unexpected on a relatively mild diesel, but another factor when shopping for tyres.

I'm glad to have it back. And now even warier of letting it out of my sight again; but it seems to have shrugged off a fairly dramatic impact. I celebrated getting it back by driving with the roof down, and you know what? I'd be really quite chuffed with this as a £25,000 spend - the age seems irrelevant compared to the comfort and luxury it offers. Looking forward to the rest of the month with it - just as the UK seems to be approaching lockdown...

Update 6: This would be the verdict, but everything changed

Really? I mean... REALLY?

Right now, you're probably reading this update from the comfort of your own home. Not necessarily by choice; a tiny little virus has ensured that for our own safety much of the world is under house arrest, allowed out for exercise once a day and inadvertently saving the planet by not driving polluting cars.

Coincidentally, it's been almost two months of unbelievably lovely weather, the sort of weather that a C-Class Cabriolet would utterly thrive in. The motorway commute and swift backroad blasts are enjoyed in refined, warm, open-air comfort thanks to the Aircap and Airscarf, and for 30mph urban routes a genuinely open feel with the windows down and style-free deflectors stowed away.

It's exactly the sort of weather I've been hoping for since the Mercedes arrived on Halloween, the final month of six being the payoff for getting a convertible in winter.

Except you can't go out. I can't go out. The car's been looking beautiful - it does at least get washed on the driveway - and very static in the spring sunshine. It got one leisure drive before lockdown, through the Peak District, and it demonstrated just how lovely summer drives will be with the roof down.

Since then, it's been for the MoT at a local garage - which it passed without incident, of course. As it was first registered on 30th March 2017, it wasn't clear if it would benefit from the six-month extension for lockdown, and frankly, I wanted the peace of mind knowing it had a valid MoT.

C-Class Cabriolet C 250 d Roof up, on road, Selenite Grey

Before Mercedes collected the car in May, restrictions were lifted slightly. It got a final Bank Holiday weekend drive, top-down on the motorway, and it just underlined what a thoroughly competent convertible it is - and what a lot of car you get for around £20,000 with a used one. After almost eight weeks of glorous weather it couldn't, responsibly, be used in, it was so frustrating to watch it leave.

On the other hand, driving a convertible in wonderful summer weather is always going to be 'it's really nice'. Where the C 250 d shone was the time when a C-Class Cabriolet would be at a disadvantage - grim winter commutes, where the rear-wheel drive, wide-tyred chassis remained secure even below zero, the cabin was warm and snug, and it delivered respectable economy and low running costs for the power available.

Entropy's a sad reality, and lockdown's really underlined that for many people; two months of limbo. As it departed, it was clear the alloy wheels had done that infuriating trick of corroding slightly under the lacquer - a side-effect of not being used, perhaps? Had it shown up under warranty (which, technically it would be until October normally) these would probably have been replaced. The sun's shining now, and I'm tempted to start browsing Mercedes' used-car website.

Yes, I would buy this car with my own money...

  • Depreciation has not been significant, but retail markup would make selling it after six months really daft
  • However, the Motorway valuation has gone up relative to winter prices, despite higher mileage
  • Leasing a new one would be more expensive, but I'd want to keep paying for an extended warranty with this level of tech

I am going to miss it - not just what it has been, but what it could have been. When it arrived, the diesel engine, the grey paint, black interior - none of it was the way I'd have specified it myself. My choice would have been to stretch a little more for a C 300 or C 43 AMG in blue, with porcelain leather.

Yet the torque of the C 250 d, the practicality of not maintaining a light interior, and the elegance of the grey over the 19-inch, relatively unfussy wheels really won me over. There are loads of clever, delightful lines in the C-Class Coupe and Cabriolet shape, too.

This car's retail price was £25,500 (rounded down) in October 2019. When I got a Motorway valuation at 16,000 miles, the highest offer was £18,000, the lowest, just over £12,000 (well, you've got to love a chancer). That's not £7,500 of depreciation, it's just the difference in trade prices, approved-used retail and the ground in the middle of non-franchised dealers; if nothing else the experience we had with the AdBlue repairs suggests you'll pay about the same overall and have a less satisfying experience if you buy a car like this outside the main dealer network - you might be absolutely fine, of course.

In June 2020, the Motorway buying prices range from £13,000 to just under £19,000 - despite 9,000 more miles and a used-car market in turmoil. This indicates demand for a good, low-mileage used convertible is high in summer, and retail prices will be correspondingly stronger. In short, the question of "do you buy a used convertible in winter" is yes - this backs up the assumption that you'll get a better deal.

In cash terms of 'buying and selling', the C-Class's trade depreciation suggests it's been a much better deal than buying or leasing new, but obviously if you bought retail and had to sell trade, it would be a big hit; so would getting out of a PCP or lease deal under the same circumstances. Keeping it for three years, it shouldn't lose much money at all. Although there's no direct comparison, a comparable 2013 E-Class Cabriolet will retail around £12-15,000 - we'd expect the C-Class to be around £13,500 when it's seven years old. So, roughly half the cost for four years of owning a used one, compared with owning from new to three years old.

In fact, the £20,000 in depreciation the first owner's taken (probably paid at £650/monnth in leasing costs), means picking up the approved-used model makes immense sense. If you want a diesel, the C 250 d is definitely worth seeking out, though if your budget will stretch to a 2018 model the improved tech overall is preferable.

Over five months of tough commutes and horrible weather, it's been a thoroughly competent and affordable car to run as well; you can find these for less than £20,000 if you buy carefully - an absolute bargain for the sophistication on offer - though the extended warranty is a must for AdBlue equipped diesels. It's also very affordable - essentially 1/2 a tank of fuel a month, or less than difference between the same commute in a C 250 d vs C 300 petrol.

In summer, it will shine. Whoever buys this one when it returns to the dealer network, I'll be very envious of them.

Mileage: 23,520
Fuel economy: