Engine coolant stops your car's engine from overheating. It's important to check your coolant and top it up if required. Failure to do so could result in a breakdown.

Engine coolant is mixed with water and antifreeze. When it comes to basic car maintenance, you should check your engine coolant at least twice a year.

Here we’ll help you to identify any problems with your engine coolant or coolant system by looking at everything from different coolant formulas, to how often you should check it and what to do if you suspect something is wrong.

How do you check your engine coolant step-by-step video?

Check your vehicle handbook for the location of the coolant filler cap – the advice given may vary from car to car.

Always ensure the engine is cool before you open the filler cap – pressurised hot water can build up inside.

Make sure the coolant is between the min and max marks on the side of the tank.

What is engine coolant?

Engine coolant is a water-based liquid which keeps your car’s engine from overheating by regulating the temperature. The coolant itself is a mixture of ethylene or propylene glycol and water, usually in a 50/50 ratio.

Running your engine produces a great deal of energy which is converted into either power – to move the vehicle forward – or heat.

While some of the heat energy is expelled via the exhaust, the remaining heat energy stays inside the engine.

Coolant flows through passages in the engine and absorbs this heat. It is then transferred to the car’s radiator where it is cooled down by air flow as the car moves.

If the vehicle is stationary, a fan will maintain the airflow to reduce the coolant’s temperature.

How regularly should you check your engine coolant?

You need to check your engine coolant at least twice a year before summer and winter, ideally. Although, this advice may vary between car manufacturers.

Coolant should be topped up whenever the level drops below the guide marks. Most modern cooling systems are sealed and do not require topping up.

However, if you have noticed any car dashboard warning lights or messages on the dashboard relating to coolant or engine temperature, you should check for leaks and if necessary, take your car to a garage for investigation.

If these warnings appear whilst driving, you should stop the vehicle when safe to do so and call for assistance, to prevent potential damage to the engine.

Always refer to your owner's handbook for the vehicle manufacturer's advice and instructions. If you don’t have a manual, you may be able to download it from the manufacturer's website.

How often should engine coolant be changed?

Engine coolant should be changed in accordance with your vehicle's manufacturer guidelines. This can be after a minimum of 30,000 miles depending on how old your car is and its make/model.

If you notice any rust or discolouring in your coolant – it will need to be changed straight away.

Can you top your coolant up with water?

Coolant should only be topped up with water in case of an emergency when the coolant liquid level is lower than it should be.

While topping up with water will help you get safely to the nearest RAC Approved Garage and identify any issues, it shouldn’t be relied upon. If you are struggling with car maintenance - contact your local mobile mechanic.

Adding a little water to coolant shouldn’t do any real damage but adding too much will lower its boiling point and stop the coolant from working as efficiently.

• Regular car checks to help prevent a breakdown and keep you safe
• Car dashboard symbols and meanings – warning lights guide
• What to pack in your emergency breakdown kit
• Book an oil chanage

What is antifreeze?

Engine coolant is also commonly referred to as antifreeze. While coolant is used to maintain the engine’s temperature all year round – most good quality coolants also have anti-freeze properties to keep the coolant functioning in sub-zero temperatures.

Always check the label of products. ‘Coolants’ will usually come pre-mixed with antifreeze and are ready to use straight away. This is why the names ‘coolant’ and ‘antifreeze’ are often used interchangeably.

Other ‘antifreeze’ liquids will need to be diluted with 50% water before use or as the label dictates.

Antifreeze also helps prevent scale build up and corrosion inside passages.

How do you know if there is a problem with your engine coolant?

Your dashboard thermometer will start to show a hotter than normal reading – meaning your car engine is overheating. The thermometer light on your dashboard will also activate.

While it could mean your coolant is leaking – this isn’t always the case.

Firstly, check if the coolant levels are lower than they should be. If the level is too low – look for leaks on all hoses, clamps and seals.

The older the vehicle, the more susceptible parts of the hoses and seals will be.

If you find your coolant level repeatedly falls below the guidelines this usually indicates a leak.

Other causes of coolant running down could be a loose radiator cap which is allowing it to escape, a faulty warning sensor or a blocked radiator. Take your car to a garage if you need a service, repair, or general advice. 

Whether you’re able to spot the source of the issue or not, it’s important to take your vehicle to be checked over as soon as possible if you find your coolant level keeps dropping.

READ MORE: Driving habits that are secretly damaging your car

What should you do if you think your car is overheating while you’re driving?

Firstly, you should switch off the air conditioning as this puts extra strain on the engine. Driving in stop start traffic will only exacerbate the problem so do your best to keep the car moving smoothly until you can get to a safe place to stop or to a mechanic.

Always wait for the engine to cool before opening the bonnet and checking coolant levels.

If your MOT is due or if you would like to book your vehicle in for a full car service, you can book online with your local RAC Approved Garage today.