Engine Coolant Explained: What It Does and How to Check It

 Most drivers know that the engine needs coolant, but few know what it really does. It's not just there to stop the engine boiling over in summer. It also protects it from freezing, from rust and from damage inside the cooling system. Checking it takes two minutes.

A quick look at the coolant level takes two minutes.

What coolant does

Coolant (also called antifreeze) carries heat away from the engine to the radiator. It also stops the liquid freezing in cold weather, protects metal parts from corrosion, and helps keep the water pump working smoothly. Old coolant slowly loses these protections, which is why it needs changing.

How to check the level

1. Park on level ground and let the engine cool down completely.
2. Find the coolant reservoir under the bonnet. It's a see-through container with MIN and MAX marks. Your manual shows where it is.
3. Check that the level is between MIN and MAX.
4. If it's low, top up with the type of coolant your manual specifies, and keep an eye on it. A level that keeps dropping points to a leak.

The one rule that matters: never open the radiator cap or the coolant cap while the engine is hot. The system is under pressure, and hot liquid can cause serious burns.

Don't mix types

Coolant comes in different colours, such as green, orange, pink or blue, but the colour alone doesn't tell you which type your car needs. Different types can react badly when mixed, and the result can clog the system. Use what the manual says. Many coolants are sold ready mixed, and concentrates need to be mixed with distilled water as the label says.

Signs of trouble

A temperature gauge that climbs, a sweet smell, a puddle under the car, white smoke from the exhaust, a heater that doesn't get warm, or a low coolant warning. If you notice any of these, don't ignore them. Coolant is toxic to people and pets, so clean up any spill and keep containers closed. Take old coolant to a garage or a recycling point.

Hybrid and electric cars

Many have separate cooling circuits for the battery and the electronics, sometimes with their own coolant. Don't top those up yourself unless your manual says you can. Leave that to a technician.

General information only. Check your owner's manual, and ask a qualified mechanic if you're not sure.