Back To Basics: Coolant checks

Rob Hawkins discusses the essentials of maintaining an engine’s coolant and how and when to renew it.

An engine’s cooling system usually consists of a water-based liquid that flows around waterways inside the engine. The liquid is air-cooled by an external radiator and recirculated by a mechanical pump to help maintain the engine’s temperature. The liquid coolant is a mixture of water and antifreeze, which helps to prevent it freezing in cold weather and causing internal damage. It also helps to prevent internal corrosion throughout the year and overheating in hot weather.

A pressure cap on the top of the radiator or expansion tank, helps to raise the boiling point by an additional 25°C by increasing the pressure in the cooling system as the engine warms up, releasing that pressure when the engine cools down. And this pressurised system reduces the risk of the coolant expanding and leaking out when it warms up, although some cooling systems have an overflow tank to collect the extra coolant when it warms up and draw it back in when it cools down.

An engine’s cooling system should be regarded with the same degree of importance as its oil. Its level should be routinely checked and if it needs topping-up at regular intervals, the cause of coolant loss must be found. Coolant has a particular lifespan before its effectiveness is reduced, so it needs to be drained and refreshed at the recommended service intervals.

The following pages provide an overview of checking an engine’s cooling system, draining and refilling it and how to identify or avoid typical problems.