How to top up engine coolant

Topping up coolant is simple — but the order and the mixture matter. Never open a hot system.

📅 Aug 17, 2026 ✔ Free guide

The cardinal rule

Never open the radiator cap when the engine is hot. Pressurized coolant at 90 °C+ can boil out and cause severe burns. Wait for the engine to cool.

How to top up

Wait for the engine to be cool
Check the expansion tank level between MIN and MAX
Use the correct coolant type for your car (OAT, G12, etc.)
If topping up, a 50/50 mix of the correct coolant and distilled water is the norm
Replace the cap and run the engine; check the level again

If you are topping up often

Frequent top-ups mean a leak or an overheating issue — check hoses, the radiator, the water pump and the thermostat. See the cooling diagnostic tool.

Questions about this guide

In an emergency, distilled water is far better than nothing, but it removes corrosion protection and freeze protection. Replace it with the correct mixture as soon as possible.

Avoid mixing types — they can react and clog the system. Use the type the manual specifies.

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