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Engine overheating: what to do and what causes it

Updated 22 Oct 2026

Driving on with an overheating engine can cause expensive damage, such as a blown head gasket. Stop as soon as it's safe.

Right now

  • Pull over safely and switch off the engine.
  • Never open the radiator cap while the engine is hot. The coolant is under pressure and can scald you.
  • Wait until the engine has cooled before checking the coolant level in the reservoir.
  • If you must move a short distance, turning the heater to full can draw some heat away from the engine.

Common causes

  • Low coolant, often from a leak in a hose, the radiator or the water pump. Look for drips or a sweet smell.
  • Radiator fan not working, so the engine overheats in traffic but is fine on the open road.
  • Blocked or damaged radiator, or a stuck thermostat.
  • Head gasket problems: white smoke from the exhaust, coolant disappearing with no visible leak, or milky oil.

What to tell the mechanic

When it happens (in traffic, on the highway, or both), whether you've been topping up coolant, and any smoke, smells or warning lights.

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