If you own a diesel car, have you noticed that there’s smoke coming out of its exhaust? Perhaps you see when you’re starting the car, particularly in cold weather, or there’s smoke when accelerating.
If any of this is currently happening to your car, then unfortunately it’s probably a sign that something is wrong with it. In most circumstances, no visible smoke should come out the exhaust of diesel cars.
Visible smoke coming from diesel cars can be tied to various mechanical issues, depending on the colour of the smoke itself. In this guide, we discuss the different types of smoke that could come out of diesel car exhaust, what issues they’re connected to and how to fix the problem.
White Smoke
Causes of white smoke
White smoke can be a result of raw diesel coming out of a car’s exhaust before it has been burned properly. This could be occurring either because the engine’s fuel injects are faulty, or as a result of low cylinder compression. The latter issue can be put down to a problem with engine valves, the engine’s piston rings or the cylinders.
If white smoke is coming out your diesel car’s exhaust while the vehicle is idle during a cold start (starting the engine at the ambient temperature) and it then disappears as the car is accelerating and the engine warms up, this could be an issue with the engine’s piston rings or the cylinders.
White smoke can also be created if water is entering combustion spaces, including faulty head gaskets or cracked cylinder blocks.
How to prevent it
You should be able to stop white smoke from being emitted during cold starts if you apply a flush cleaner to the engine, to reduce dirtiness of key components. This product should be available from car maintenance stores.
If this isn’t enough to stop white smoke being emitted and it’s a fault with engine components, then you should take your diesel car to a professional garage. Be prepared to pay for repairs in this scenario.
Blue Smoke
Causes of blue smoke
Blue smoke can potentially be emitted during a cold start when the car is idle because oil is being burnt. This could be as a result of an issue with the engine oil itself. The oil put in the car may be the incorrect grade for the engine, meaning it’s too thick or thin to run the engine properly.
Alternatively, oil could be getting burned because of problems with one or several engine components including the valve guides or seals, the piston rings or the cylinders.
How to prevent it
Similarly to how you stop white smoke from being emitted, using a flush cleaner on your diesel car’s engine may be exactly what’s required to reduce blue smoke being emitted.
If blue smoke is still coming out after you’ve used this though, then that indicates a more serious engine issue that you should get checked at a garage.
Black Smoke
Causes of black smoke
Of all the different colours of smoke that can come out of a diesel car’s exhaust, black smoke is the most common type. It is usually a sign of inadequate and unfinished incomplete combustion of the diesel fuel.
There are many potential causes for this, including dirty or worn fuel injectors, a faulty turbocharger, worn or sticking piston rings, a dirty air filter or the engine could be operating at a below average temperature.
Over fuelling or using a poor quality fuel can also lead to black smoke being emitted.
How to prevent it
Making sure you buy decent quality fuel from non-suspect outlets and regularly check that the air filter is not too dirty. These are good to ways to reduce the chances your diesel car will ever emit black smoke, or put a stop to it if it’s already happened before.
Engine components may to need to be restored to full cleanliness from time to time, which you can do using a flush cleaner on the engine itself. If the air filter is filthy then it’s relatively easy to replace yourself.
If black smoke is being emitted even when you take all of these precautions, then it’s likely tied to other engine components. In that case, it makes sense to get a mechanic to inspect the engine and make necessary changes.
