Checking your engine coolant

Stop your car overheating

Engine coolant is a mixture of water and anti-freeze that helps to stop your engine overheating.

Most modern cars have a sealed cooling system so they shouldn’t need topping up. Unless, of course, they’ve sprung a leak.

Check your engine coolant every couple of weeks so you can spot any problems early. It could save you a lot of money and hassle.

How to check your coolant

Many modern cars will have a dashboard warning light to let you know if there's a problem with your coolant. You should get your car checked at a garage if the warning light comes on.

If you need to check it or top it up manually, here's what to do.

1. Find the expansion tank

  • Make sure you find the right tank (adding antifreeze to the screen wash, brake fluid or power steering reservoir could cause damage).
  • Check your vehicle handbook to find the location of the coolant filler cap.

2. Check the engine coolant level

  • The coolant should be between the min and max marks on the side of the expansion tank.
  • Low engine coolant can also cause problems with your car heater. A symptom of this could be cool air coming from the dashboard vents even when the dial is set to ‘hot’.

3. Check hoses for problems

  • Check any hoses that you can see at the same time.
  • Wet or white staining is a sign of possible problems to come.

4. Top up if necessary

Important: Only do this when the engine is cold.

  • If the coolant needs topping up, don't remove the filler cap unless the engine is cold – you could be scalded by a sudden release of pressurised hot water.
  • Make sure you use the right antifreeze – different types don't mix well.
  • Antifreeze doesn't just protect your engine in winter. It helps stop corrosion and scale build-up all year round.

5. Take it to a garage

  • It's not normal for the coolant level to drop.
  • If you see that it's dropped, get a garage to take a look.

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Engine coolant

What is engine coolant?

Coolant is a liquid that's added to a car's engine cooling system. It's usually a dilution of antifreeze and water.

It stops the water in the system from freezing under normal cold weather conditions and it also raises its boiling point.

Along with a pressurised system, this helps to reduce the risk of overheating.


Can you put water in coolant?

Important: If topping up, only do this when the engine is cold.

It's not advised to add water to your engine coolant, unless the coolant level is lower than it should be and it's an emergency.

Topping up your coolant with a bit of water is okay to help you get your car to the nearest garage.

If the dilution level is left too weak over the winter, the water in the cooling system could freeze and cause engine damage.


What coolant does my car need?

There are different types of engine coolants on the market, also called antifreeze. It's important to buy the right one for your vehicle.

Learn more about checking the right coolant for a car.


What is a cooling fan?

When your car's moving, air flows through the radiator to keep your engine's temperature 'normal'.

But if you stop – in a summer traffic jam, for example – your engine relies on its cooling fan to force air through the radiator. The fan's controlled by an electric thermostat and your car's engine management system.


How to check your coolant fan

Cooling fans in car engines should start up automatically. If they don't there may be a fault with the fan temperature sensor, the wiring or the fan itself.

Ask your local garage to give it the once over if you think there's a problem or your car is overheating.

Here's a step-by-step guide showing how to check your cooling fan.

Woman looking at overheated engine with steam coming out

How do cars overheat?

If you never check your car's coolant level, you could face a hefty repair bill if your engine overheats.

At best it could be a couple of hundred quid to repair the cooling fan, more than that to replace the head gasket, or at worst, it could be over a four-figure sum for a new engine.


Why do engines overheat in the summer?

Overheating is a much bigger problem during the summer than in the winter:

  • Engines operate at higher temperatures in summer.
  • There isn't the cold winter air to take away a lot of the heat.
  • The cooling system is tested more when you take it on a long trip or get stuck in a summer traffic jam.

Many cars are only used on local journeys. On short trips, the engine barely reaches normal operating temperature, so the cooling system isn't tested.

However, that changes when the car's suddenly loaded with luggage and passengers for a long summer trip in hot weather, which is when problems in the system can show up.

Find out how breakdown cover can help you if you have car trouble:

How to avoid your engine overheating

Here's what you can do to keep your engine cool:

  • Check your coolant level using our simple steps.
  • Check your cooling fan – a seized cooling fan is the most common cause of initial overheating. Make sure the engine is cold and switched off. Electric cooling fans can switch themselves on even when the keys are removed. If you're not sure what to do, call us. Or you can get your garage to carry out a full cooling system test.
  • If the temperature gauge rises, the best way to temporarily deal with it is to turn the heater up full and the air conditioning on.

Try to get into the habit of regularly checking your car, including the coolant level and fan.

Modern cooling systems shouldn't really need topping-up between services. So if you notice that the coolant has dropped, get it checked out. For 24/7 Roadside Assistance, you can get breakdown cover from our Patrols.

Published: 14 April 2016 | Updated: 13 October 2022 | Author: The AA

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