Originally Posted by TygerCub
I've seen a couple of posts lately (one of which was mine) that asked "why does my bus smoke?" One of the responses said there were three colors of smoke, and each one indicated a different problem. I figured this was the best forum to ask this question:
What does WHITE smoke indicate & how can it be fixed?
What does BLUE smoke indicate & how can it be fixed?
What does BLACK smoke indicate & how can it be fixed?
Here are some textbook answers.
White Exhaust Smoke
white smoke could indicate several problems, such as unburned fuel from lack of heat, incorrect injection timing, poor atomization of fuel or coolant being burned during combustion.
White Smoke Due to lack of heat
. When fuel is injected into a combustion chamber where there is insufficient heat for ignition and combustion the fuel will not be completely burned resulting in White Smoke. Low ambient temperatures (Winter Operation) make it more difficult for cylinder pressure to generate enough heat, especially when starting the engine. Once the engine has warmed up the smoke will normally disappear. Starting aids are used to reduce this problem (Glow plugs, intake heaters etc.) Low compression pressures (worn engine) will not generate sufficient heat for efficient combustion and can cause the engine to produce white smoke even at operating temperature.
White Smoke Due to Incorrect Injection Timing.
If the fuel injection timing is retarted, the burning fuel chases the piston down in the cylinder. When the exhaust valve opens, the heat escapes before the fuel is completely burned. The unburned or partially burned fuel exits the exhaust as white smoke. With the engine at operating temperature and under load, the white smoke may appear to be a gray color.
White Smoke Due to Poor Atomization of Fuel
Poor atomization of the fuel may be caused by low injection pressure. The fuel droplets are too large and therefore harder to ignite and burn. As a result combustion is in complete resulting in White Smoke.
Black Exhaust Smoke
Black exhaust smoke usually indicates there is not enough oxygen for proper combustion.
Black Exhaust Smoke Can be The Result of Two Conditions.
1. A lack of air for the metered amount of fuel. This could be due to a plugged air filter, a defective turbo or leaking intake system gaskets and hoses on turbo charged engines.
2.An excess amount of fuel (overfuelling) for the amount of air an engine can supply. If the maximum fuel setting is greater than the manufacturers specs or if pollution controls have been improperly adjusted, there may not be sufficient air to burn all of the fuel.
Blue Exhaust Smoke
Blue exhaust smoke is the result of an engine burning oil. Common causes include worn piston rings, excessive crankcase pressure, worn valve guides or a defective turbo charger.