Show Me, Tell Me: Engine Coolant

"Where would you check the engine coolant level, and how would you know if there is enough?"

The engine coolant, as its name suggests, prevents the engine from overheating. The system consists of a radiator, mounted at the very front of the engine bay behind the grill, an expansion tank which allows the coolant to expand as it gets hot, and pipes circulating the coolant around the engine. The top half of the expansion tank must be just air, for the expansion to take place safely!

The system is refilled via a cap on top of the expansion tank; this must never be removed while the engine is hot, as it could be under considerable pressure

Some cars have a temperature gauge inside, showing you the temperature of the engine:

The needle will rise into the normal zone when you have been driving for a while; it must not go into the red. If your car does not have a gauge, then a warning light will come on if the engine overheats. DO NOT ignore the warnings: your engine may seize up or even explode, which would cost you many thousands of pounds!

To check the coolant level, open the bonnet and look for the expansion tank. On most vehicles it will be similar to this:

The symbol represents an old-style car radiator, from a bygone era when the filler cap was located on the radiator and there was no expansion tank; some may instead use something like this:

Probably more appropriate for modern cars!

As I said above, the expansion tank must have air in it, to give the heated coolant room to expand; often there will be markings for maximum and minimum, and the level should be between the two:

Alternatively, as a guideline, the level should be around the centre of the tank:

If the level is low, you should top up with a universal coolant which contains anti-freeze, diluted as recommended on the bottle; you can buy this at any petrol station or car parts seller. It is also fine to use water in the summer, but it is worth having the strength of the anti-freeze checked by a garage at the start of the winter, so that your engine doesn't freeze and potentially crack.

If you have an older car there will be no expansion tank; you would need to check the level by removing the radiator cap, and filling to the top.

For your test, the answer to the question is that you open the bonnet, point at the expansion cap, and say that it must be between maximum and minimum markings.

As with all fluid levels, you should check every week or two, and before any long journey.