Engine coolant is a mixture of antifreeze and water and regulates the temperature of the water in your engine, to ensure that your car does not overheat or freeze throughout the year.
Nearly one third of the energy produced by a car engine ends up as waste, either through the exhaust or as excess heat energy. This excess heat energy must be cooled quickly to prevent the engine overheating.
To do this, coolant is pumped through the closed loop system, absorbing the excess heat from the engine and carrying it through the radiator. Air flowing through the radiator then removes the heat from the coolant and the cycle starts again.
The temperature is controlled by a thermostat in the engine that controls the flow and in modern cars the system will change along with the external conditions.
When should coolant be changed?
The coolant/antifreeze itself does not expire but the substances in it that prevent engine corrosion do. Each manufacturer will have their own recommendations for when coolant should be changed, this averages at about every 30,000 miles.
It’s always good to keep coolant at home or in the boot of your car, and to check that your coolant level is still within the minimum and maximum levels on the reservoir under the bonnet. You can easily top coolant up yourself at home but be careful not to confuse this with washer fluid as they are two very different fluids.
Can’t you just use water?
Coolant is mainly made up of water, with each car manufacturer having their own set of guidelines of the correct ratio of water to antifreeze. However, topping up your coolant with more water is okay on the odd occasion when the level looks a bit low. When doing a full change or larger top up though, you should use the recommended amounts.