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What does different coloured exhaust smoke mean?

26th September 2023

Your exhaust’s job is to convert harmful gases created during combustion into less harmful ones, and disperse them into the atmosphere, meaning that the smoke coming from your car’s exhaust should be barely noticeable. However, If you do see smoke coming out of your exhaust, don’t panic.  

Here at Merityre, we offer free exhaust health checks, so simply book in at your nearest branch and our specialists will be on hand to diagnose the problem. Want to know more about what different coloured smoke coming out of your exhaust could mean? Our guide explains what the different colours could mean along with the potential causes. 

Why is white smoke coming out of my exhaust?

White smoke coming from your exhaust could be caused by a number of reasons depending on when it occurs and what it smells like. Some of the causes of white smoke coming from your exhaust could include: 

  • Condensation: In cold weather conditions it can be quite normal to see white smoke coming out of the exhaust when you start the engine. It is caused by water vapour in the exhaust and should dissipate fairly quickly as the system heats up. 
  • Coolant leak: If the white smoke does not dissipate quickly, and you continue to see it as you’re driving - not just when you’re starting your car. It could indicate a coolant leak into the combustion chamber, often you’ll be able to tell if coolant is leaking as the smoke will give off a sweet smell.  
  • Engine issues: Some engine issues can lead to white smoke coming out of your exhaust due to a poor mix of air-to-fuel ratio. There are several potential causes of this including problems with the fuel injection system, sensors or engine control unit.  

Why is black smoke coming out of my exhaust?

Black smoke coming out of your exhaust is often due to the extra production of carbon. Causes of this can include: 

  • Rich air-to-fuel mix: This means that there is an excessive amount of fuel being injected into the combustion chamber compared to the air available. This can occur due to issues with the fuel injection system, such as malfunctioning fuel injectors, a faulty fuel pressure regulator or a sensor problem. 
  • Clogged air filter: A clogged air filter restricts the airflow into the engine, disrupting the right air-fuel mixture. This can lead to incomplete combustion and the production of black smoke. 

Reminder: Our gold service checks the condition of your air filters and replaces them if necessary. Book your gold service here. 

  • Excessive Carbon Build-up: Carbon deposits can accumulate on various engine components over time, including the combustion chamber, fuel injectors, and intake valves. This build-up can disrupt the combustion process and lead to the production of black smoke. 
  • Burning rubber: Black smoke coupled with an acrid smell could be a sign of something seriously wrong with your car, as it is a sign of rubber or plastic components burning and your vehicle overheating. 

Why is blue smoke coming out of my exhaust?

Blue smoke is typically a sign that oil is being burned in the combustion chamber. This might occur for several reasons including:  

  • Worn piston rings: Piston rings are responsible for maintaining the proper seal between the piston and the cylinder wall. When they become worn or damaged, they can allow oil to leak into the combustion chamber which is then burned giving off blue smoke. 
  • Worn valve seals: Valve seals are responsible for preventing oil from entering the combustion chamber through the valves. If these seals deteriorate or become damaged, oil can leak past them and be burned during the combustion process. 
  • Cylinder wall wear: Excessive wear on the cylinder walls can lead to increased oil consumption and oil entering the combustion chamber. 
  • Overfilling your vehicle with oil: Overfilling your engine with oil can cause an oil overspill causing the excess oil to be burned.  

What to do if coloured smoke is coming out of your exhaust

If you experience smoke coming out of your exhaust accompanied by other symptoms such as loss of power, unusual noises or overheating, you should pull over safely, turn off the engine and assess the situation. 

Many issues that cause coloured smoke are due to issues with fluids. You should check and monitor your oil and coolant levels as well as check if these fluids are contaminated as this could be a sign of a potential issue.  

If you have any worries concerning your exhaust, contact your nearest Merityre Branch. Coloured smoke is often a sign of underlying engine or exhaust system problems, it’s vital that you do not ignore it as it could lead to further damage to your engine and potentially more expensive repairs in the future. Book a free exhaust check and our qualified mechanics will accurately diagnose the problem and recommend necessary repairs.