What do different colours of exhaust smoke mean?

Author Name – Jack Underwood

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More often than not when driving you may notice that the car in front is expelling smoke coming from the exhaust. As petrol and diesel cars have internal combusting engines it is normal for a bit of smoke to be visible. However, if there is a continuous stream then this may be cause for concern. There are many variables that can cause this continuous stream of smoke coming from the exhaust and these can be further narrowed down by the colour of the smoke. In this article, we are going to run down the different colour smoke that comes from the exhaust and what this may show about the condition of your vehicle.

Look at the following infographic identifying the different types of smoke

exhaust smoke infographic

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White smoke

On the contrary to a temporary thin white smoke being expelled from the exhaust being normal, a continuous thicker white smoke causes more reason to be alarmed.  This form of smoke is most likely the result of your car’s coolant leaking into the exhaust.  This could be caused by a faulty head gasket or a cracked cylinder head or engine block. 

Blue smoke

Blue smoke is another indicator that there is a mechanical problem with your car.  A burning smell often accompanied by blue smoke coming from the exhaust indicates that engine oil is burning. Engine oil is responsible for lubricating vital moving parts of your engine, ensuring that they do not get damaged or overheat. Some reasons for engine oil burning could be worn cylinder walls, leaking value seals or damaged piston rings. After getting a service you may notice this smoke. If it goes after a short while, it is excess oil burning off and is no cause for concern.  

Black smoke

Black smoke is another abnormal smoke coming from the exhaust. This is an indication that your car is burning too much fuel. This problem only applies to diesel and petrol vehicles and there are multiple reasons why this may be taking place. It could be due to a malfunctioning fuel injection system, a blocked manifold or damaged piston rings.

Temporary thin white smoke

When it comes to smoke coming from the exhaust, the only normal type of smoke to expect isn’t actually smoke at all. When first starting your engine, especially on a cold morning you may see a thin white layer of water vapour. This is a result of condensation build-up within the exhaust as the car begins to warm up. This thin layer of water vapour should eventually disappear, any continuous smoke that does not eventually disappear can indicate a problem internally in your car.

What should I do if I notice a continuous stream of coloured smoke?

If you notice that your car is expelling any of the smoke labelled in the infographic it is essential that you get your vehicle seen by a professional straight away. Even if your car is in working order it is recommended that you visit a garage as prolonged use of the car whilst there is one of the possible issues listed will result in further complications down the line, you may also be likely to break down possibly putting yourself and other drivers at risk.

Will coloured smoke lead to a failed MOT?

A new rule has been listed for MOT checks, that if a car has a continual stream of smoke coming from the exhaust this will lead to an automatic fail. Around 6% of cars that enter an MOT check will fail due to this. This is often because it indicates a mechanical fault or a failed emissions test.

Related: Car service & MOT

Where can I get this fixed?

At national we have over 250 nationwide branches with professionals that can identify the problem causing the coloured smoke coming from your vehicle and fix this issue.  Whilst getting this issue fixed, we recommend that you get your vehicle serviced to ensure that there are no more problems and you can drive away feeling secure that your car is working to its full capabilities.

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