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Smoky vehicles

Fixing your smoky vehicle

Smoky exhausts add to air pollution. If your vehicle's exhaust produces excessive smoke, check the cause and have your vehicle serviced or repaired.

Diesel engines should not produce continuous smoke as long as they are correctly maintained, driven sensibly and quality fuel is used.

Possible causes of smoke

An image of a smoky vehicle.Some factors that can contribute to causing smoke include:

  • how the car is serviced
  • how the car is driven
  • engine wear
  • fuel quality
  • engine design
  • pollution control equipment
  • the length of a journey.

Even properly adjusted and maintained vehicles can produce visible smoke at maximum power during gear changes, while carrying a heavy load, or after a period of idling.

If your vehicle produces smoke continuously for 10 seconds or more, this means that something is wrong and needs fixing.

Types of smoke

Smoke from vehicles is generally caused by unburnt or partly burnt fuel. Burning engine oil can also cause a smoky exhaust.

Black smoke is generally caused by incompletely burnt diesel fuel.

Blue, white and other coloured smoke is generally caused by burning engine oil or unburnt fuel vapour. Easily seen, blue smoke is usually caused by a serious engine fault.

Faults that can cause smoke

These are just some of the faults that can cause smoke. Not all of them apply equally to petrol and diesel engines.

Faults that can cause smoke include:

  • an overfilled sump
  • a blocked air cleaner
  • faulty fuel enrichment systems used for cold starts
  • faulty electronic or mechanical controls
  • poor fuel quality (contaminated or incorrect density or grade)
  • a blocked or damaged fuel filter
  • incorrectly set or damaged fuel injectors or fuel pump
  • worn piston rings, pistons, cylinder bores, valve stems, seals or guides
  • incorrectly set or damaged turbochargers or superchargers.

Smoky vehicles pollute the air. Next time you see a vehicle blowing smoke continuously for 10 seconds or more, please report the smoky vehicle.

Last updated
24 August 2017