Smoke coming from the car exhaust can signify there is a serious problem. To identify the problem, you'll need to look at the color of the smoke. Here are the main colors you will likely see along with possible causes. Knowing this information will help you get an idea of what is wrong so you can give the mechanic a heads up.
White smoke often occurs when hot engine smoke hits cold air. This is normal, and it will usually occur when you have had the engine running for some time. However, if you are seeing white smoke for another unknown reason, it could signify a leak in the car's head gasket or a blockage or crack in the cylinder head. These are common problems that will be picked up with a typical car service. The white smoke appears because there is coolant getting into your exhaust and it is being vaporized.
In a diesel car, the white smoke means your car is not burning the fuel effectively. It could be due to incorrect timing within the engine or an overheating engine.
Blue smoke in a gasoline automobile is usually a sign that the pistons need to be changed. It could be either the rings, cylinders or valves—or all of them depending how long this has been a problem. The blue smoke is due to the oil burning within the car exhaust, usually through the piston rings or valves.
Piston damage or wear and tear is also a reason for blue smoke in diesel cars. However, could also just be a sign that there is just too much oil within the system.
Black or Grey Smoke
These are the colors most people notice early on, and they are a sign of numerous problems. One problem is that the fuel combustion may be incomplete, whether you have a diesel or gasoline car. Other potential problems include a faulty carburetor or a malfunctioning emission system. The air filters may be clogged or the manifold blocked. Oil is possibly leaking into the exhaust. In a diesel car, black or grey smoke may indicate that the engine is overheating or the wrong fuel grade has been used.
When you notice smoke blowing from your car exhaust, take a note of the color. This will be used by the mechanics at your car service to help identify the initial possible causes.