Back in the 2010s, diesel cars accounted for half of all new cars sales in the UK. They reached that level popularity because of their great fuel economy and the tax benefits of their low carbon dioxide emissions. But, in 2024, diesel was just 6.3% of the market, which may leave you wondering whether you should buy a diesel or petrol car, especially as the market shifts towards electric cars.
It’s an interesting question and, as ever, there’s a lot of nuances to consider. Despite the government-mandated push towards electric cars, petrol still makes up the majority of the new car market, taking 52.2% of sales in 2024. Electric cars accounted for 21.4% of sales, plug-in hybrids 18.3% and other hybrids 9.6%, with diesel bringing up the rear.
Clearly, there’s an ever-smaller place in the world for diesel cars, but there may be a place for one in your life. Here, we’re going to consider the relative merits of diesel and petrol cars to help you decide if diesel still works for you. But first, let’s quickly cover exactly how diesel cars work and why sales have dropped off a cliff.
What’s the difference between petrol and diesel?
The difference between petrol and diesel engines isn’t as complicated as you might think. Both are internal combustion engines that produce power by burning a mixture of air and liquid fuel. The difference is in now you get the fuel to burn.
In a petrol engine, the fuel is burned by compressing it, then igniting it with an electrical spark generated by the spark plug. In a diesel engine, the fuel is burned by compressing it, then it’s ignited by a constant heat source – the glow plug. In some of the latest diesels, the glow plug isn’t needed – the fuel is compressed until it essentially spontaneously combusts.
Why have diesel sales dropped so drastically?
Diesels became hugely popular in the 2000s off the back of tax incentives based on their low carbon dioxide emissions. The decline started in 2015 with ‘dieselgate’, the scandal in which Volkswagen was caught cheating in emissions testing of its diesel cars. That threw sharp focus on the fact that diesels emit high levels of various harmful chemicals in their exhaust emissions, particularly oxides of nitrogen.
At around the same time, cities around the world – including London – realised they had a real problem with poor air quality. Testing showed that harmful emissions from diesel engines were a large factor, so measures were put in place to penalise diesel drivers and discourage them from driving into those cities.
Add in the impending ban on the sale of new petrol and diesel cars from 2030 and diesel sales in the UK have dwindled to a very small proportion of the car market. It’s not just the UK, either. Diesel sales across Europe and much of the rest of the world have cratered, as well.
It’s worth noting that the latest diesel cars have exhausts fitted with diesel particulate filters filters and other systems that scrub harmful emissions out of the exhaust gases. The result is that their emissions almost match those of petrol cars.
So, having covered that, let’s get into the main question.
Why should I buy a diesel car?
Diesel cars have many appealing benefits. Let’s have a look at some of the key ones.
Diesel engines tend to be much more fuel efficient than an equivalent petrol engine, by as much as 50% in some cases. You particularly notice the difference in high-speed motorway driving.
Diesel engines produce a lot more torque (pulling power) than an equivalent petrol engine. That means they’re well suited to big, heavy cars such as large SUVs, and are better for towing trailers. They can also cruise at high speeds more easily than petrol engines.
Being more fuel-efficient means diesel cars can go further between fill-ups than an equivalent petrol car – not to mention hybrids and electric cars. For example, the Mercedes E450d diesel can go nearly 700 miles on a single tank of fuel, while the hybrid E300e only manages 450 miles. If you do lots of long journeys, that extra 250 miles could be really valuable.
The values of older diesel cars fall rapidly, however there is some evidence that newer ones are holding onto their value pretty well. That’s partly because diesels that meet Euro 6 emissions standards aren’t excluded from any UK low emissions zones and, as we’ve discussed, diesels are becoming increasingly rare. There will always be a hardcore of drivers who favour diesel, so the simple forces of supply and demand may well keep diesel values buoyant.
Why shouldn’t I buy a diesel car?
There are some negatives to consider with diesel cars, as well. Here are some of the most significant ones to consider.
Diesel fuel costs more than petrol and new diesel cars usually cost to buy more than petrol equivalents. Diesel cars are, of course, more fuel efficient, but that difference in purchase and running costs means you have to do a lot of miles to save money on the higher running costs of a petrol car.
Diesel cars have complex high-pressure fuel injection, turbochargers and emissions control systems that need scrupulous maintenance to prevent them developing reliability issues. They also don’t like doing lots of low-speed, stop-start driving, which can clog them up with soot and gunk. A regular long drive that gets the engine up to operating temperature helps keep the systems clear.
Diesels with manual gearboxes can have other issues, as well. They’re often fitted with a dual mass flywheel, which helps smooth out the engine’s vibrations. However, they wear out and need replacing every 100,000 miles or so. The clutch needs to be replaced at the same time, as well, leaving you with a bill well into four figures.
Older diesels that don’t meet Euro 6 emissions standards incur a charge of entering all UK low emissions zones (LEZ); in Europe, diesels are excluded entirely from some LEZs. You can check on the government website whether your car in incurs a charge in places like London and Bristol; Continental journeys will require more in-depth research. Check out our list of the best LEZ-compliant diesels.
Diesel fuel has a strong, distinct smell that some people may not like – we recommend always wearing gloves to fill up. And diesel cars are usually louder than petrol ones when idling and at low speed, producing a sound that can grate on some people.
How are diesel cars to drive?
Diesel cars are rarely the sharpest of knives on a country road because their engines are heavier than a petrol equivalent. However, they’re often fantastic long-distance cruisers. That’s because diesels have more torque and rev lower, which can make them more relaxed at high speed. They’re usually better able to haul up a long hill and tend to accelerate quicker at intermediate speeds – from 40 to 70mph, for instance.
Small diesel engines can sound a bit noisy and clattery, but the big six- and eight-cylinder diesels found in luxury SUVs and saloons often sound fantastic. They feel really muscular when accelerating, as well, a sensation we always find deeply satisfying.
Can I still use my diesel car after 2030?
Sales of new cars powered purely by petrol and diesels will be banned in the UK from 2030. But there is no threat to such cars already on the road so, if you have a diesel car, you’ll be able to keep using it long after 2030.
How long? Only time will tell. There’s no suggestion that liquid fuels such as diesel will be banned this century, however filling stations may become rarer as the number of electric vehicles increases. How long diesel fuel remains readily available may depend on how quickly the haulage industry switches to alternative fuels. Synthetic diesel may become available at some point, as well.
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