What is antifreeze?

Antifreeze is a clever liquid that plays an important role in keeping your car's engine in good health. But for it to work as it should, you need to use the right kind in the right concentration.

Here's our go-to guide for all your questions on antifreeze.

What is antifreeze?

Antifreeze is a liquid that's added to a car's cooling system. It stops the water from freezing under normal cold weather conditions.

As well as lowering the freezing point, it also raises the boiling point of engine coolant. Along with a pressurised system, this helps to reduce the risk of overheating.

Is coolant the same as antifreeze?

Antifreeze and coolant are similar, but not exactly the same. Antifreeze is a concentrated product, normally based on glycol and containing inhibitors. Some types of antifreeze have to be diluted with water at a suitable concentration before you use it. Once the antifreeze is diluted with water, it becomes coolant.

Why does my car need antifreeze?

Modern car cooling systems are smaller, with higher operating temperatures and pressures than in the past. That means it's especially important to use the correct additive.

If you don't use antifreeze, you could suffer serious damage to your car's radiator and other components if the water freezes or overheats. Water expands as it freezes which can spilt radiators or even break engine casings.

This vital liquid helps your engine in other ways too. It prevents scale building up and protects against corrosion, helping to keep your car healthy.

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What antifreeze for my car?

The correct type of antifreeze for your car should be shown clearly in the vehicle handbook along with advice on recommended concentrations.

Without a handbook to refer to, you should check with a dealer. You can also find out more about coolant on our coolant advice page.

How do I find out what type of antifreeze is in my car?

If you don't know what type of antifreeze is in your vehicle, it's not easy to identify it without sophisticated tests. The colour of the antifreeze isn't proof of the type or quality of product that was used.

If you're worried you've used the wrong type of antifreeze, it's best to take it to a professional mechanic who'll drain and flush the system. Antifreeze is a hazardous substance, so you should never attempt this yourself. Once it's empty, it can be refilled with the recommended type of antifreeze at the correct dilution level.

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What are the different types of antifreeze?

Antifreeze solutions are typically available in two different types, ethylene-glycol or non-toxic propylene glycol. In terms of colour, there are different antifreeze mixes for different types of engines. Antifreeze's were originally bright green, but you might come across yellow, green, red or blue antifreeze mixes, all with different anti-corrosive factors.

Where can I buy antifreeze?

You can buy antifreeze from motoring supply shops and most petrol stations if you're out and need to top up immediately. Alternatively, you can buy antifreeze online, but remember to check your vehicle's handbook to make sure you're purchasing the right type.

Can you put water in antifreeze?

Antifreeze is mixed with concentrated water to make coolant, but if you want to top up the antifreeze in your car because it's running low, then adding water is not the best solution. Water can be used to top up the antifreeze in your car in an emergency, but this could also cause damage if left for too long. The best idea is to get your antifreeze topped up with the proper solution.

Does the car need to be running when adding antifreeze?

No, your engine should be off when adding antifreeze. Don't add antifreeze right after a long drive though, as the engine parts in your vehicle will still be hot. Make sure your engine has been off long enough for your car to cool down before topping up with antifreeze.

Adding antifreeze to a hot engine could damage your vehicle and could also lead to personal injury.

Is it ok to drive with low antifreeze?

No, you should top up your antifreeze as soon as you become aware that it's getting low. Some cars will have a dashboard warning symbol for low antifreeze, which looks like a thermometer in water (or like a radiator). Driving on with low antifreeze could result in permanent damage to your engine.

How do I check my antifreeze strength?

The strength of your antifreeze can be measured using a hydrometer or a refractometer. Hydrometers are easier to use but can be less accurate.

Most garages should have these tools and be able to check for you.

I want to replace or top-up the coolant. What should I use?

For replacing or topping-up antifreeze, you should use the product recommended by the vehicle manufacturer or one that meets the specification set by them.

It is important when using concentrate to make sure that it's diluted to the correct mix with good quality water. You also need to wait until the engine is cold before topping up.

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Does sludge form when different types of antifreeze are mixed?

Good quality antifreeze shouldn't form sludge even when different types are mixed. Problems with sludge tend to happen with poorer-quality coolants or the use of very hard water (or both).

However, you should avoid mixing different types of coolant as it could make the corrosion inhibitors less effective and could leave the coolant in a gel-like state.

The stuff the handbook says I should use is too expensive – can I use something cheaper?

For most people, a car is a big investment. In comparison, the price of even the most expensive antifreeze or coolant is relatively minor. Purchasing a good quality antifreeze or coolant will help to protect that investment.

Using a cheaper, inferior product could result in expensive damage to the cooling system or the engine and prove to be a false economy in the long run.

I care about my car – can I use a premium coolant or antifreeze instead?

While the vehicle is in warranty, you should use only the vehicle manufacturers' recommended fluids.

When out of warranty, use an antifreeze or coolant that meets the same specification and renew at the recommended intervals.

What is propylene glycol and who uses it?

Propylene glycol (PG) based antifreeze or coolant is offered by a number of suppliers as a less-toxic alternative to ethylene glycol based products.

Good quality PG products perform very similarly to ethylene glycol based products. They're used by people who are worried about the toxicity of ethylene glycol based products.

Only some vehicle manufacturers currently use PG based products for original fill. But PG based products are more widely used in Austria and Switzerland where there is legislation that restricts retail sales of hazardous products.

Do some vehicle manufacturers still use a high silicate antifreeze or coolant?

Currently, no vehicle manufacturers use high silicate products. For today's technologies, silicates are just one of many potential corrosion inhibitors.

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