How long does coolant last?
Coolant is deeply important. It’s the liquid tasked with coursing through your engine to keep it cool and corrosion-free. It also works its way through the interior heater matrix to keep the cabin warm.
Take a look at your car’s handbook for coolant change intervals. Some older models – including classics – need a change every two years. They require what's known as Inorganic Acid Technology coolant, which is kinder to the seals and gaskets used on older engines. It's typically blue in colour but is becoming harder to find in shops. Don't be tempted to swap it for longer-lasting 'Organic' coolant (see below), because it's likely to damage your classic's seals.
Modern vehicles can go for 10-15 years or even more with the fluid they come out of the factory with – you may see 'lifetime coolant' referred to, which is often (but not always) pink in colour. This coolant is also known as Organic Acid Technology. Once you change this 'factory fitted' coolant for aftermarket coolant, we'd recommend renewing it every five years, unless the instructions on the bottle say otherwise.
Whichever coolant your car needs, we'd recommend checking its strength each autumn, and certainly before cold weather arrives, to make sure it's still at sufficient strength to protect your vehicle from a deep freeze.
However, if you're changing a part that's connected to the cooling system, such as the water pump, you'll need to replenish some or all of the coolant well before these intervals.
Can’t I just use water?
Your engine needs coolant. You should never, ever just put water in your cooling system. Water on its own will course through your engine and do nothing to prevent corrosion. The coolant additive you put into your engine is chemically balanced to react in certain ways under certain conditions.
In winter, the additives in coolant prevent it from freezing. Use plain old water and it'll freeze in your engine block. Water expands when it freezes, which will crack the block. And that’s game over.
Those additives also raise the coolant's boiling point, to prevent the engine from overheating, particularly when it's working harder if you're towing or in hot weather.