How often to change coolant (antifreeze)

Coolant (often called antifreeze) stops the engine freezing in winter, raises the boiling point in summer and protects the cooling system from corrosion. It does not last forever, but how long it lasts depends heavily on the car.

In the schedules below, intervals range from about 30,000–150,000 miles50,000–240,000 km depending on the maker and model. That is why the only reliable answer is in your owner's manual or service book.

Intervals vary a lot by maker

Long-life coolants have stretched intervals a long way, but the numbers still differ widely. Some examples from published schedules:

• Hyundai: most models get a first change at 60,000 miles100,000 km, then roughly every 30,000 miles50,000 km after that (Cars.com).
• Mercedes-Benz: it depends on the model and engine. Some call for a change at 30,000 miles50,000 km, others at 120,000 miles190,000 km or 12 years, and some at 150,000 miles240,000 km or 15 years (Cars.com).
• General Motors (DEX-COOL): a 2007 GMC Canyon manual says the coolant is designed to last five years or 150,000 miles240,000 km, whichever comes first, if you only add DEX-COOL. The same manual says it may need changing sooner, at 30,000 miles50,000 km or 24 months, in some conditions.
• UK general advice: the RAC says to follow the manufacturer's guidelines, which can mean a change after a minimum of 30,000 miles50,000 km, depending on the car's age and model.

Two things to watch:

• Time limits count too. Most schedules say "miles or years, whichever comes first". A low-mileage car can still be due.
• Severe use. Some makers ask for more frequent changes if you tow or drive in harsh conditions. Check the "severe service" section of your schedule.

Some garages recommend changing coolant every 30,000–50,000 miles50,000–80,000 km, more often than many makers ask. Cars.com notes that a garage can test the coolant with test strips and a hydrometer, so you only change it early if it has actually stopped protecting the engine.

Never open a hot radiator cap

The cooling system runs under pressure. If you open the cap on a hot engine, scalding coolant can spray out. The RAC warns that pressurised hot water builds up inside.

• Wait until the engine is cold before you open the cap or the coolant tank.
• If the temperature light comes on or the gauge goes into the red while you drive, pull over safely and switch off. See our engine temperature light guide.
• If the car is overheating, do not keep driving to "make it home". Our guide to why your car is overheating explains what to do.

How to check the coolant level

The RAC suggests checking at least twice a year, ideally before summer and before winter.

1. Park on level ground with the engine cold. First thing in the morning is easiest.
2. Find the coolant expansion tank. It is a translucent plastic bottle, usually with a warning symbol on the cap. Your owner's manual shows where it is.
3. Read the level on the side of the tank. It should sit between the MIN and MAX marks. Some tanks have a separate COLD mark: use that one when the engine is cold.
4. Top up if it is below MIN, with the coolant type your manual specifies. Pre-mixed coolant goes straight in. Concentrate usually needs mixing with water, often 50/50; follow the label.
5. Do not overfill. Stop at the MAX line.
6. Look at the colour. Rust, sludge or a murky, discoloured look means it is time for a change, whatever the mileage.

If you have to top up more than once, look for a leak. Our guide to a car leaking water helps you tell coolant from harmless condensation.

Don't mix coolant types without checking

Coolants use different corrosion-inhibitor chemistry, often labelled IAT, OAT or HOAT. Prestone warns not to mix OAT and IAT coolants unless you are sure they are compatible, because it can cause serious damage. GM's manual warns that using a coolant other than DEX-COOL may cause early corrosion of the engine, heater core or radiator.

• Check your owner's manual first. It lists the coolant specification your car needs.
• Don't go by colour. The same colour can be different chemistry, and the same chemistry can come in different colours.
• If you are unsure, a "universal" top-up product or a little water can get you to a garage in an emergency. Then have the system drained and refilled with the right coolant.

DIY or garage?

Keep it simple

• Look up your car's coolant interval in the service schedule, in both miles and years, and note it in our service tracker.
• Check the level cold, a few times a year.
• Only add the coolant type your manual names.
• Never open the cap on a hot engine.