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Steam From Under The Bonnet

Steam from the engine bay usually means coolant is boiling or leaking onto hot parts. The engine may be overheating.

Short answer · What should I do if steam comes from under the bonnet?

Stop as soon as it is safe and switch off the engine. Do not open the coolant cap and keep away until the steam stops. Let the engine cool for at least 30 minutes, then check the coolant level. Driving on with an overheating engine can cause serious damage.

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Safe checks you can do

  1. Stop and switch offTurn on hazard lights and leave the bonnet closed while it steams.Hot coolant and steam can cause severe burns.
  2. Wait for it to coolAt least 30 minutes before touching anything.
  3. Check the coolant levelOnce cold, look for leaks and the level.

Questions that narrow it down

  1. Is the temperature gauge in the red?The engine is overheating.
  2. Does it smell sweet?Coolant leak.
  3. Is it light vapour after rain or washing?Water evaporating on hot parts can be harmless.

Possible causes

Listed without ranking. Use the questions above to see which ones fit your car.

  1. Engine overheatingCoolant boils.
  2. Burst hoseCoolant sprays onto hot parts.
  3. Failed radiator or capPressure is lost.
  4. Water on hot parts after rainHarmless vapour.

Questions about Steam From Under The Bonnet

Can I add cold water to a hot engine?

Wait until it cools. Adding cold liquid to a very hot engine can crack parts.

When is it safe to drive again?

Only after the cause is found and the coolant is at the correct level.