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Smoke Coming From Exhaust (What Different Exhaust Smoke Colours Mean)

Updated: Jan 9

Smoke from the exhaust of a vehicle is not uncommon, but it can be concerning if you are not sure what it means.


The colour of exhaust smoke can provide clues as to the cause of the issue, and understanding the different exhaust smoke colors can help you determine if there is a problem that needs to be addressed.


  • White exhaust smoke is due to water vapour and is typically caused by the engine burning coolant.

  • Grey exhaust smoke is due to incomplete combustion and can be caused by ignition or fuel issues.

  • Blue exhaust smoke is typically caused by the engine burning oil and can be caused by worn engine parts.

  • Black exhaust smoke is due to unburnt fuel leaving the exhaust and is usually caused by the engine running rich or exhaust system issues.


This article is a detailed breakdown of what the different exhaust smoke colours mean, including why smoke may be coming out of your exhaust and whether or not it is safe to continue driving.

 

Table of Contents:


smoke coming from a car exhaust

Why Is Smoke Coming Out of My Exhaust?

There are several potential reasons why smoke may be coming out of your exhaust. One common reason is that the engine is burning oil. This can happen if the engine is worn out or if there is a problem with the oil system, such as a leak.


Another reason for smoke from the exhaust could be a problem with the fuel system, such as a clogged fuel filter or a malfunctioning fuel injector.


In some cases, smoke from the exhaust may be the result of a problem with the exhaust system itself, such as a leak in the muffler or catalytic converter.


Why Does Exhaust Smoke on Startup?

It is normal for there to be a small amount of smoke from the exhaust when starting a cold engine. This is usually due to condensation that has accumulated in the exhaust system and is burned off as the engine warms up.


However, if there is a significant amount of smoke on startup or if the smoke persists after the engine has warmed up, it may be a sign of a problem.


Smoke From the Exhaust While Accelerating

If you notice smoke coming from the exhaust while accelerating, it could be a sign of a problem with the fuel system or the engine itself. In particular, this type of smoke may indicate a problem with the ignition system or a malfunctioning fuel injector.


It is important to have the issue checked out by a mechanic to determine the cause and take appropriate action.


White Exhaust Smoke

White exhaust smoke is typically caused by coolant that is burning in the engine. Coolant is a fluid that is used to regulate the temperature of the engine and prevent it from overheating.


When coolant is burned in the engine, it can create white smoke in the form of water vapour that is visible in the exhaust.


There are several potential causes of white exhaust smoke, including the following.


  1. Head gasket failure: The head gasket is a seal that sits between the engine block and the cylinder head. It is responsible for sealing the combustion chamber and preventing coolant and oil from mixing. If the head gasket fails, coolant may leak into the combustion chamber and be burned, creating white smoke.

  2. Crack in the engine block: A crack in the engine block can allow coolant to leak into the combustion chamber and be burned, creating white smoke.

  3. Faulty thermostat: The thermostat is a valve that regulates the flow of coolant through the engine. If the thermostat is faulty, it may not open or close properly, causing the engine to run too cold or too hot. This can result in coolant being burned in the engine, creating white smoke.

  4. Blocked radiator: The radiator is responsible for dissipating heat from the engine and preventing it from overheating. If the radiator is blocked or not functioning properly, the engine may overheat and cause coolant to be burned in the engine, creating white smoke.


If you notice white smoke coming from the exhaust of your vehicle, it is important to have the issue checked out by a mechanic as soon as possible.


White smoke can be a sign of a serious problem with the engine and continuing to drive with the issue can cause further damage and may even be dangerous.


white exhaust smoke coming from a car exhaust pipe

Grey Exhaust Smoke

Grey exhaust smoke may be a sign of a problem with the fuel system or the engine itself. Grey smoke is typically caused by incomplete combustion of the fuel, which means that not all of the fuel is being burned in the engine.


This can result in unburned fuel being expelled through the exhaust, creating a grey smoke. There are several potential causes of grey exhaust smoke, including the following.


  1. Similar causes as white exhaust smoke: Sometimes grey exhaust smoke can be caused by similar issues that white exhaust smoke can be caused by.

  2. Malfunctioning fuel injector: The fuel injector is responsible for delivering fuel to the engine. If the fuel injector is malfunctioning, it may not be delivering the correct amount of fuel to the engine, causing incomplete combustion and resulting in grey smoke.

  3. Clogged fuel filter: The fuel filter is responsible for removing impurities from the fuel before it reaches the engine. If the fuel filter is clogged, it may not allow enough fuel to pass through to the engine, causing incomplete combustion and resulting in grey smoke.

  4. Malfunctioning ignition system: The ignition system is responsible for providing the spark that ignites the fuel in the engine. If the ignition system is malfunctioning, it may not provide enough spark to ignite all of the fuel, causing incomplete combustion and resulting in grey smoke.


If you notice grey smoke coming from the exhaust of your vehicle, it is important to have the issue checked out by a mechanic as soon as possible.


Grey smoke can be a sign of a problem with the fuel system or the engine and continuing to drive with the issue can cause further damage and may even be dangerous.