A couple of decades ago, it wasn’t unusual to see cars parked by the side of the road with steam pouring from beneath the bonnet. By and large that doesn’t happen anymore but it’s as important for drivers to keep an eye on the level of coolant in their car as it is to check their oil.

Where is your coolant?

Coolant flows all around the engine. But it’s easy to check how much you’ve got. First, lift your car’s bonnet and you’ll probably be confronted by a daunting collection of pipes, wires, bottles and usually some plastic covers. What you’re looking for is a clear plastic bottle.

This is what’s known as the expansion tank. It’ll probably be towards the back of the engine bay and it’ll have a coloured (either blue or black) lid on it, usually with some cartoon steam embossed on it. Inside it will have a liquid that may be pink-ish, red-ish or blue. If you’re in any doubt, check your car’s user manual.

How do you check your coolant?

Look closely at this expansion tank and you’ll see there are lines with minimum and maximum written by them. The liquid should (and probably will) be between these lines. And it’s as simple as that.

What is coolant?

Coolant is a mixture of distilled water and anti-freeze. The anti-freeze will stop the water freezing at low temperatures and is a vital part of this mixture.

What if your coolant level is low?

For a start, it shouldn’t be. The coolant system is a sealed unit. Liquid may occasionally weep out and evaporate but you certainly shouldn’t have to top it up regularly. If it is low, you will need to refill it.

How to top up coolant

You must wait until the engine is cold before adding coolant. Take the top off the coolant bottle when the engine is hot and you risk being scalded with steam. Even when the engine is cold, professionals usually hold this lid with a cloth in case pressurised liquid escapes.

In an emergency you can top up coolant with tap water. However, it’s better to add a distilled water and anti-freeze mix. You can buy both from a motor retailer. If you are adding any fluid to your car’s coolant, you should use a funnel. Anti-freeze is corrosive and an irritant so you don’t really want to spill any.

The easiest is to use pre-mixed coolant. If you’re using concentrated solution, mix the correct ratio of anti-freeze to distilled water in a separate container. The anti-freeze bottle should give you an idea of the correct ratio. For the UK’s usually fairly temperate climate it will probably be 50-50 but it may be up to 70%. When you’ve topped up the level to between the minimum and maximum markers, replace the lid.

How to check your anti-freeze strength?

You don’t want the anti-freeze to become too diluted or it won’t work when you need it to. There are two ways of checking it. You can either buy a tool from a motor retailer. It’ll cost around £7 and will tell you the strength of your car’s coolant mixture. Alternatively take your car to a garage and they’ll check the anti-freeze strength for you. This should be a part of any winter check that you take your car in for.