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Smoke Signals – What Your Exhaust Smoke May Be Telling You

  • Exhausts

A car’s engine burns fossil fuels that create carbon monoxide, nitrogen oxide, and nitrogen monoxide. While the exhaust system helps reduce the air as well as noise pollution that your car produces, it also designed to ensure that these harmful toxic gases are safely emitted out of and away from the vehicle.

In a properly working system, the exhaust manifold funnels gases from all cylinders, and in petrol-driven engines, releases a thin, white smoke composed mainly of water vapour through the exhaust pipe. However, when that smoke changes to a different colour or thickness, it may be trying to tell you something is wrong.

Causes of Exhaust Smoke in Petrol Engines

Normal exhaust emission is light and thin and is no cause for concern. It is composed mostly of water and usually only noticeable on cold days, typically when starting up your car or while the engine is still warming up.

Colour Diagnosis

  1. White vapour – If it’s thin and light, this is normal and common in petrol-driven vehicles. If the outside temperature is cool, condensation can build up inside the exhaust system and heat inside the pipes give off steam.
  2. Thick white-grey – This is likely engine coolant burning due to it leaking out as a result of any of the following:
    1. Blown head gasket or leak in the head gasket
    2. Damaged cylinder head
    3. Cracked engine block

Leaking coolant can cause your engine to overheat resulting in serious damage.

  1. Blue-grey – Often accompanied by a burning smell, it’s possible that there is an oil leak, either caused by leaking valve seals, damaged piston rings, or worn cylinder walls, and the engine is burning oil. Small leaks can be managed easily enough but extensive damage will be expensive to repair so it’s best to have your car checked out as soon as possible.
  2. Grey – Like blue smoke, this could be a sign of burning oil. There are many possible reasons your exhaust is emitting thick grey smoke, such as:
    1. Excessive oil consumption
    2. PCV valve failure
    3. Transmission fluid leak (automatic gearbox)
    4. And more
  3. Black – In petrol-driven engines, a clogged air filter can cause the car to burn too much fuel. So can a clogged fuel injectors, a clogged fuel line, a blocked manifold, or damaged fuel-pressure regulators.


Not only does a car’s exhaust system draw gases safely out and away, it’s also an important component that enables your car to run quietly, smoothly, and efficiently. If your exhaust starts emitting smoke, don’t ignore the signs – you could be saving you and your car from the risk of costly damages.

Make use of Supa Quick’s free vehicle safety check* and have your exhaust checked for problems such as leaks, noises, vibration, and burning smells. Visit your nearest Supa Quick service centre for your exhaust fitment needs.

*List of component checks varies from dealer to dealer.

Disclaimer: This content is for informational, educational, or entertainment purposes only. We do not make any warranties about the completeness, reliability, and accuracy of the content.


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