There are two main reasons why a diesel engine produces excessive amounts of fumes and toxic substances, vital engine parts are worn or misadjusted.
Smoke is caused by too much fuel for a given amount of air or engine oil burning in the combustion chambers. Excessive emissions are caused by poor fuel condition.
Secondly, white smoke at start-up, emitted by some engines when cold, is most likely considered a malfunction of the internal parts of the engine. Many of the fumes or emissions related faults listed may sound familiar and add to the list of faults previously described.
Smoke types
Generally speaking, there are three types of smoke that can indicate engine problems. Of course, if the engine has more than one type of fault, more than one type of smoke will be seen.
Black (or dark gray) smoke
It is a symptom of incomplete combustion of fuel in the engine and can be caused by low combustion pressure and temperature (this is the reason why the diesel engine smokes when starting) as well as other malfunctions listed below. Part of the burned fuel comes out in the form of soot particles.
White or grayish white smoke
Caused by incomplete combustion of fuel in the form of vapor or evaporation of engine oil. It is also possible for coolant to leak into the combustion chambers through cracks in the cylinder head or through a damaged cylinder head gasket; this produces steam, which can be confused with white smoke. Smoke persists and has «oil» smell, and the steam quickly disappears and is practically odorless.
Blue or bluish gray smoke
Caused by the combustion of engine oil in the combustion chambers as a result of engine failure, excess engine oil, or the wrong type of engine oil being used. If the engine is checked with diagnostic equipment, visual smoke limits can be applied to some older engines (depending on engine operating conditions), but for new engines it is necessary to make accurate measurements of the characteristics of fumes and emissions.