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?

What does antifreeze do?

Antifreeze is a glycol-based liquid (usually ethylene glycol or propylene glycol) that's added to a car's cooling system. It stops the water from freezing under normal cold weather conditions.

Antifreeze also includes various additives that provide additional benefits, such as corrosion inhibition, pH balancing, and anti-foaming properties.

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

What’s the difference between antifreeze and coolant?

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 are required to be diluted with water at a suitable concentration before you use it. Once the antifreeze is diluted with water – usually 50/50 – 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, your car's engine and other components could suffer serious damage if the water freezes or overheats. Water expands as it freezes, which can split radiators, pipes and water pumps 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’s cooling system healthy.

Finding the right antifreeze for your car

What are the different types of antifreeze?

Antifreeze solutions are typically available in two different types, ethylene-glycol or non-toxic propylene glycol.

There are different antifreeze mixes for different types of engines, identified by different colours:

1. Green or blue (Inorganic Acid Technology – IAT):

• Properties: Traditional antifreeze, typically used in older vehicles.
• Lifetime: Usually needs to be changed every 2 to 3 years or 30,000 miles.
• Additives: Contains silicate and phosphate corrosion inhibitors.

2. Red or orange (Organic Acid Technology – OAT):

• Properties: Commonly used in modern vehicles with extended-life formulations.
• Lifetime: Can last up to 5 years or 150,000 miles.
• Additives: Contains organic acids for corrosion protection, without silicates or phosphates.

3. Yellow or gold (Hybrid Organic Acid Technology – HOAT):

• Properties: A hybrid of IAT and OAT, combining the benefits of both.
• Lifetime: Typically lasts around 5 years or 150,000 miles.
• Additives: Contains silicates for added protection, along with organic acids.

4. Pink or purple (Phosphated Organic Acid Technology – POAT):

• Properties: Often used in specific brands and types of vehicles, including some Asian makes.
• Lifetime: Can last up to 5 years or 150,000 miles.
• Additives: Contains organic acids and phosphates for corrosion protection.

5. Blue (Silicated Organic Acid Technology – Si-OAT):

• Properties: Common in European vehicles, particularly Volkswagen and Audi.
• Lifetime: Typically lasts around 5 years or 150,000 miles.
• Additives: Contains silicates and organic acids for enhanced protection.

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.

What type of antifreeze do I need 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.

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How to add antifreeze to your car

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’s important when using concentrate to make sure that it's diluted to the correct mix with good quality water (distilled water). You also need to wait until the engine is cold before topping up – this is to prevent injury when opening the cooling system.

Never open the coolant cap when the engine is warm, or when the vehicle is running.

Learn why low coolant levels might be the reason your car heater's not working. 

Where do I put antifreeze in my car?

On most modern cars, antifreeze goes in the coolant reservoir – you’ll find this under the bonnet. Look for a translucent plastic tank with a cap labelled ‘coolant’ or ‘antifreeze’. It might also have a symbol that looks like a thermometer in liquid. In some older cars the antifreeze may go directly into the top of the radiator.

How do I know when I should add antifreeze to my car?

Some cars will have a dashboard warning symbol for low antifreeze, which looks like a thermometer in liquid (or like a radiator).

You can also check the level of liquid in the coolant reservoir. Look out for the ‘MIN’ and ‘MAX’ marks on the side – if the liquid is below the ‘MIN’ mark, it needs to be topped up.

Check your coolant levels at least twice a year: before it starts to freeze in winter, and before temperatures starts to soar in summer.

Can I 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 you could also injure yourself, too.

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. Driving 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 will be able to check for you.

Which antifreeze to buy

The antifreeze recommended by my car’s handbook 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. Buying 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.

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 it at the recommended intervals.

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.

You can also buy antifreeze online – but remember to check your vehicle's handbook to make sure you're getting the right type. 

What is propylene glycol, and who uses it?

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

Good quality PG-based 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. They're more widely used in Austria and Switzerland, where there’s 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.