Check your coolant regularly

You might spot a leak before it causes a breakdown

How to check your coolant


It's important to check engine coolant level regularly – weekly if possible – it's not hard to do.

The level shouldn't change unless there's a leak somewhere.

And if there is a leak, it's much better discovered early and at home, rather than in the outside lane of a motorway when the engine overheats.

We show you how

Overheating can cause real damage to your car's engine. This simple video by AA Patrol Nick Evers shows you how to keep your coolant at an optimum level and prevent overheating.

The coolant must contain the correct concentration of anti-freeze as well, not just for winter protection but for year round protection against corrosion and scale build up which can reduce the efficiency of the cooling system.

Checking the expansion tank

The car's radiator is fitted with an ‘expansion tank’ that allows the coolant to expand under rising pressure and temperature. This is usually clear plastic so you can see the level inside, and marked with maximum and minimum marks.

If you're topping up the coolant level it's essential that you identify the expansion tank correctly - adding antifreeze to the screen wash, brake fluid or power steering reservoir would be a very bad idea.

Check the vehicle handbook for the location of the coolant filler cap, and follow any vehicle-specific advice given.

  • Only check the coolant level when the engine is cold - it should be between the maximum and minimum marks
  • Check regularly and look out for wet or white staining on coolant hoses too
  • Refer to the handbook to make sure you use the correct type of antifreeze and follow the correct procedure
  • Don't remove the coolant filler cap unless the engine is cold – the system is pressurised and you risk a face-full of scalding hot water if you release it with the engine hot
  • If the level drops in a modern car's sealed cooling system the coolant must be escaping from somewhere - get a garage to investigate.

Checking the cooling fan

In normal driving, airflow through the radiator keeps the engine temperature stable but when ambient temperatures are high and the vehicle is stationary for some time, the temperature will start to rise. Thermostatically controlled cooling fan(s) mounted on the radiator help to maintain the correct engine temperature in these conditions but it's important to check that they operate correctly.

Follow this simple procedure to check the operation of the cooling fan(s):

  • Set the car heater to cold
  • Run the car to normal temperature
  • Allow the engine to idle for around five minutes
  • Watch the temperature gauge - don't allow the car to overheat

The fan should cut in automatically - if it doesn’t there may be a fault with the fan temperature sensor, the wiring or the fan itself.

(Updated July 2013)