Quick answer
Tick what you are seeing. Puddles or crusty residue usually mean an external leak; white sweet smoke, milky oil or bubbles point to an internal leak such as a head gasket; a sweet smell inside the car suggests the heater core. Stop driving if the engine overheats.
Key takeaways
- External leaks leave puddles or crusty residue.
- Smoke, milky oil or bubbles suggest an internal leak.
- If the gauge is high, stop and let it cool.
Confirm the specification in your owner’s manual before buying. Product examples are not a fitment guarantee.
On this page
What are you seeing?
Tick everything that applies.
Guidance only. A cooling-system pressure test and a combustion-leak test give the real answer.
How the troubleshooter works
Each symptom points towards a few common causes. The tool scores them and shows the most likely first, with the guide that explains the next check. It does not replace a pressure test.
Quick checks you can do (engine cold)
- Check the reservoir against the MIN and MAX marks, and note the level.
- Look under the car after parking overnight on a clean surface.
- Look for crusty residue on hoses, clamps, the radiator and around the water pump.
- Check the oil dipstick and filler cap for milky residue.
- Watch the reservoir with the engine idling for bubbles (do not open the cap when hot).
When to stop driving
- The temperature gauge is in the red or a red coolant light is on.
- Steam from under the bonnet.
- White sweet smoke together with a falling coolant level.
See also: low coolant · coolant leaks · coolant warning light.
Frequently asked questions
Why am I losing coolant but there is no leak?
It can leak onto hot parts and evaporate, escape through a worn cap, leak into the cabin through the heater core, or leak internally (for example a head gasket). The troubleshooter helps narrow it down.
Can I keep driving if I am losing coolant?
Only short distances while the temperature stays normal and you keep it topped up. Stop if the gauge rises or the warning light turns red.
Does coolant evaporate?
A sealed system should not lose a meaningful amount. Regular top-ups mean there is a leak somewhere.