What is antifreeze? And how to check your engine coolant level

We explain how antifreeze keeps your engine from overheating, and why you should regularly check your levels

Hibernation feature - Antifreeze

As the name suggests, the primary function of antifreeze is to prevent your car's coolant from freezing in low temperatures (with coolant being a combination of water and antifreeze). All liquid-cooled cars depend on antifreeze to keep going in cold weather and there are a number of different types to choose from. So In order to understand what antifreeze is, first you need to know where it goes and what it actually does.

The varying colours of the fluid - usually pink/red, blue, or green - are the most obvious sign that there are, in fact, a variety of antifreeze types but all undertake the same crucial job. They prevent the coolant from freezing, allowing it to continue carrying excess heat away from the engine, dispersing it via the radiator and keeping the engine at the optimal operating temperature.

Coolant works to prevent the engine from overheating when the engine is running, but when you switch the engine off, the coolant stops flowing and temperatures drop down. This is where the antifreeze comes into play, especially in colder climates, as it works to prevent the water in the mixture from freezing and expanding. If the coolant were to expand, this could cause a range of problems, including leaks or even a warped cylinder head.

On top of lowering the freezing point of the mixture, antifreeze also serves another purpose - it acts as a lubricant/protector for the engine internals. Most engines are made from either iron or aluminium, and both materials which can be corroded by water. Therefore, modern antifreeze coolant contains chemicals which protect the internals of an engine from corrosion - including the water pump, which is often located in awkward places that make repairs expensive.

What are the different types of antifreeze?

As with many fluids for your car, there are a number of variants of antifreeze to choose from. An antifreeze’s type depends on the ingredients on which it is based. Two of the most common types are Inorganic Additive Technology (IAT) and Organic Acid Technology (OAT). Different cars will require different types of antifreeze, as the wrong type could lack the protective qualities that your engine needs, causing premature wear or damage. So, as always, the best way to check which type of antifreeze is correct for your vehicle is to either refer to the owners’ handbook or ask your local motor factors, dealer, or garage.

How do you check your car's coolant level?

There are two common ways to do this, and it depends on the cooling system your car has. Firstly, there are systems which have a coolant reservoir that allows the coolant level to change as the system heats up without dumping fluid. To check the level of a system like this, follow the steps below:

Check engine coolant on cars with a reservoir

  1. Let the engine cool completely as the system becomes pressurised under use.
  2. Use your handbook to locate the position of the coolant reservoir in the engine bay.
  3. Open the bonnet and locate the coolant reservoir, if you do not have the hand book, it is normally on one side of the engine over a wheel arch.
  4. On one side of the reservoir there will be a minimum and maximum mark to indicate where the level of the coolant should be (these are usually for when the coolant is cool), use these to check the level of the fluid.
Hibernation feature - Antifreeze

Check engine coolant on cars without a reservoir

There are also systems which do not have a reservoir. They may have an overflow tank where water can be released to, but it cannot return to the engine.

  1. Similar to above, let the engine cool completely as the system becomes pressurised under use.
  2. Open the bonnet and locate the radiator - it is usually at the front of the engine. If you cannot find it, fall back to the car’s handbook for instructions.
  3. Get a rag or old tea towel and carefully undo the cap on top of the radiator. If you have not waited long enough for the engine to cool, steam may be released, so be careful.
  4. With the cap removed, look into the radiator, the coolant should be up to the top.

If your coolant is below the minimum, you will either need to top it up, or even better, drain the system and replace the coolant. A mechanic will be more than happy to replace your engine coolant for you, and it should be a reasonably inexpensive job.

If you decide to do the work yourself, there are a couple of things to bear in mind. Firstly, most modern cars have completely sealed systems, meaning coolant should only need replacing if there has been a leak, so it may be worth investigating that first. Also, the different types of antifreeze do not mix and can have adverse effects on your car, so make sure you get the correct one. 

Have you had any cooling-related horror stories? Let us know in the comments below...

Recommended

How to check and top up your engine oil
How to check and top up oil - header
Tips & advice

How to check and top up your engine oil

Your car’s engine oil shouldn’t be neglected. Here’s how to check and top up your engine oil
8 Jun 2021
Locking wheel nuts explained: types, removal and lost keys
Ford Tourneo Custom wheel detail
Owning a car

Locking wheel nuts explained: types, removal and lost keys

We explain how locking wheel nuts work, and what to do when you lose your locking wheel nut key...
19 May 2021
Best car wheel wax and sealant
Best wheel sealant - header
Product group tests

Best car wheel wax and sealant

Which is the best spray-on car wheel sealant treatment to keep brake dust and grime at bay?
11 May 2021
Best cordless vacuum cleaners 2021
Best vacuum cleaners
Product group tests

Best cordless vacuum cleaners 2021

Which cordless vacuum cleaner is the best making light work of filthy interiors?
11 May 2021

Most Popular

Driving test update to preserve the manual gearbox
Dacia Duster gear lever
News

Driving test update to preserve the manual gearbox

With more drivers learning in autos and electric cars, the DVSA is looking to update the driving test so people can still drive manuals in future
16 Jun 2021
UN report highlights ethical problems with electric cars
Electric car charging
News

UN report highlights ethical problems with electric cars

Analysis reveals lithium refining takes 65 per cent of Chilean region’s water, while 40,000 child miners dig for cobalt in DRC
14 Jun 2021
Fiat 500 vs MINI Electric vs Honda e
Fiat 500 vs Honda e vs MINI Electric
Car group tests

Fiat 500 vs MINI Electric vs Honda e

The new Fiat 500, MINI Electric and Honda e are three retro-inspired electric superminis - but which is best?
19 Jun 2021
New Audi Q4 e-tron 2021 review
Audi Q4 e-tron 2021  front
Audi Q4 e-tron

New Audi Q4 e-tron 2021 review

We get involved with the new all-electric Audi Q4 e-tron SUV on UK roads for the first time
17 Jun 2021
Ineos Grenadier prototype 2022 review
Ineos Grenadier prototype
Ineos Grenadier 4x4

Ineos Grenadier prototype 2022 review

Can the Ineos Grenadier really fill the mud-splattered void left by the old Land Rover Defender? We take a first drive in a prototype to find out...
15 Jun 2021
Fan-designed Ford Puma ST Gold Edition revealed
Fan-designed Ford Puma ST Gold Edition
Ford Puma

Fan-designed Ford Puma ST Gold Edition revealed

Ford unveils a special edition Puma ST, with a black and gold colour scheme chosen by Ford fans over social media
18 Jun 2021
New Nissan Qashqai 2021 review
Nissan Qashqai 2021
Nissan Qashqai

New Nissan Qashqai 2021 review

We get behind the wheel of the larger, more comfortable and higher-tech Nissan Qashqai SUV in the UK
16 Jun 2021
New 2021 Vauxhall Astra to offer plug-in hybrid power
Vauxhall Astra render
Vauxhall Astra

New 2021 Vauxhall Astra to offer plug-in hybrid power

The new Vauxhall Astra will get a plug-in hybrid powertrain and a more premium image - here’s how it could look
17 Jun 2021
New 2021 Hyundai Tucson N-Line hybrid and PHEV on sale now
Hyundai Tuscon N Line - front
Hyundai Tucson

New 2021 Hyundai Tucson N-Line hybrid and PHEV on sale now

Hyundai names price for new Tucson N-Line hybrid duo with plug-in offering 38 miles of electric running
18 Jun 2021
New Skoda Enyaq iV 2021 review
Skoda Enyaq iV 80 Sportline - front
Skoda Enyaq

New Skoda Enyaq iV 2021 review

The new Skoda Enyaq iV is the Czech firm’s first bespoke electric car and we've tested the full range on UK roads
10 Jun 2021
Tesla Model 3 police car all set for evaluation by UK emergency services
Tesla Model 3 police car - front
News

Tesla Model 3 police car all set for evaluation by UK emergency services

Tesla hopes to offer UK police forces a new zero-emission emergency responder option with the Model 3 police car
17 Jun 2021
Motorists think they can get away with driving offences due to lack of road police
police speed gun
News

Motorists think they can get away with driving offences due to lack of road police

Lack of road traffic police officers in the UK is making it easy for drivers to break the law, according to a survey of 15,500 British motorists
16 Jun 2021
'The hydrogen underdog disruptor is back in town'
Toyota Mirai opinion
Opinion

'The hydrogen underdog disruptor is back in town'

Mike Rutherford says hydrogen-powered cars could still be a frequent sight on UK roads
13 Jun 2021
New Mercedes-AMG S 63 spied in minimal camouflage
Mercedes-AMG S 63
Mercedes S-Class

New Mercedes-AMG S 63 spied in minimal camouflage

AMG will soon launch a tuned version of Mercedes’s flagship limousine, probably powered by a 603bhp twin-turbocharged 4.0-litre V8 engine
18 Jun 2021