There are many vital fluids your car needs to run properly, including engine coolant. It’s one of the most important but one that’s often overlooked during servicing, which can have catastrophic consequences. To help avoid that happening, it’s useful to understand exactly what engine coolant is, why it’s so important and how to check during routine car checks.
You may hear people refer to an engine’s antifreeze or water, but they’re actually talking about coolant. However you refer to it, the coolant level needs to be kept topped up and all of it needs replacing periodically.
In this guide, we’re going to cover everything you need to know about engine coolant and make some recommendations on the best coolant you can get for your car, plus some gadgets that can help you keep an eye on the coolant’s condition.
What is engine coolant and why do I need it?
Engine coolant is a fluid that’s a 50-50 mix of water and antifreeze. Antifreeze isn’t just needed in winter, it’s necessary year-round. That’s because, aside from preventing the water freezing, antifreeze also raises water’s boiling point, preventing overheating.
The internal combustion engine process generates an enormous amount of heat that must be carried away from the engine, and that’s what the engine’s cooling system does. It’s a similar principle to central heating. The coolant is pumped around the engine, heating up as it goes. The hot water then flows through the radiator, dissipating the heat to the atmosphere. If there’s a failure or blockage anywhere in the system, the heat can build up and cause significant damage such as head gasket failure or even the engine seizing.
How to check your engine coolant level
It’s vital you keep an eye on the amount of coolant in your car’s engine. The level goes down slowly over time through evaporation; if the level falls quickly, there’s probably a leak in the cooling system. Fortunately, it’s really easy to check the level.
Open your car’s bonnet and look for a transparent plastic tank containing a coloured fluid. If you can’t see the fluid, look for a symbol on the cap like the one below. The tank’s exact location differs between cars – if you can’t find it, consult the manual.
On the side of the tank, you’ll see markings showing the minimum and maximum levels – better to be nearer maximum than minimum. The vast majority of modern cars show a warning light or message if the coolant level gets too low, but don’t rely on that, especially if you have an older car. The coolant level is checked and topped up during routine servicing at a garage, but you can do that yourself.
Can I refill my coolant myself?
Yes. Just lift your car’s bonnet, take the cap off the coolant tank and pour the coolant in. Make sure you replace the cap after. It best to top up when the level drops to roughly halfway between the minimum and maximum marks. Make sure you wear gloves as coolant can damage skin.
We must caution you with a warning you’ll see on the coolant tank. Only take the cap off the when the engine’s stone cold. When it’s hot, the cooling system is pressurised. Take the cap off too soon and you could get blasted by a jet of scalding hot fluid.
Which engine coolant do I need for my car?
There are several different types of coolant used in different types of car. We won’t get into the weeds on exactly what they all are here; to find which one your car needs, refer to its handbook or search online – Halfords has the best engine coolant search tool.
It’s vital you know whether you’ve bought ready-mix coolant or concentrate. Ready-mix can be poured straight into your car’s coolant tank while concentrate must be diluted with clean, plain water – make sure you read the instructions and get the proportions exactly right.
There are, of course, many different brands of engine coolant available, and some car manufacturers produce their own that are recommended for use in their engines.
Parkers' top recommended engine coolant
Pros
- Suitable for lots of cars
- Very good value
Cons
- Not the best-known brand
How much coolant do I need?
That depends on how big your car’s engine is. Small engines may only need five litres, there are some really big engines that need over 20 litres. You only need exactly the right quantity if you plan on changing the coolant yourself, otherwise a five-litre bottle will suffice for occasional top-ups.
How often does coolant need replacing?
Car manufacturers specify how many miles their engines can go between coolant changes; any garage worth its salt will do the job when the car is serviced around that mileage. However, the lifespan of coolant can vary beyond the manufacturer’s specifications depending on how the car is used. For instance, doing lots of long motorway journeys may necessitate more frequent changes. You can keep an eye on your coolant’s condition with a coolant tester.
Parkers' top recommended coolant tester
Pros
- Great built quality
- Ease of use
Cons
- Not especially sophisticated
It’s also sensible to have your car’s coolant system flushed out every so often, to clear out all the muck and crud that accumulates over time. A good garage will tell you when one is necessary, but don’t be afraid to raise the possibility.
It’s possible to DIY an engine coolant engine, but our advice is to only undertake one if you’re already reasonably proficient at car servicing. That’s because coolant is a highly caustic and toxic substance that must be handled with care and disposed of correctly.
FAQs
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Is engine coolant just water?
No. Engine coolant is often referred to as water but it’s actually a 50-50 mix of water and antifreeze. If you buy coolant concentrate to top up your car, make sure you dilute it in exactly the right proportions.
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What problems can an engine cooling system develop?
There are many components in a car’s cooling system, any one of which can fail if the car isn’t serviced properly. In many cars, the water pump that pumps coolant around the engine is essentially a disposable item, needing periodic replacement along with the associated drive belts and pulleys. The job often coincides with a cambelt replacement.
The thermostat that regulates the whole system can also fail. Radiators can become clogged up with silt and rust, its exterior surfaces can rust or get damaged, as well. And there are innumerable pipes and seals in the system that can leak. -
What happens if engine coolant is low?
If the coolant level is too low, your car’s engine will get too hot while it’s running. That could have disastrous consequences, including the engine seizing up. If that happens, the engine’s probably a write-off.
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Is engine coolant the same as antifreeze?
No. Though engine coolant is often referred to as antifreeze, it’s actually a 50-50 mix of antifreeze and plain water. Not only does antifreeze prevent the water freezing, it also raises the boiling point.
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What is waterless coolant?
Having stated several times throughout this article that engine coolant is made with a 50-50 mix of antifreeze and water, we should acknowledge that there's such a thing as waterless coolant. It's a chemical blend of various glycols including antifreeze, therefore it has precisely zero water content. Waterless coolant is favoured by many classic car enthusiasts; the lack of water means rust is unlikely to develop in a car's cooling system. However, some critics suggest it has a lower boiling point than conventional coolant, so it's less able to prevent overheating.
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