The exhaust of a working engine is practically colorless. A barely noticeable light white smoke comes out of the exhaust pipe, the intensity of which increases when you sharply press the gas pedal.
In frosty weather, a properly functioning car leaves behind quite thick clouds of white steam (not to be confused with smoke!), indicating complete combustion of the fuel.
Inhaling exhaust gases for a long time is not good for you. We turn off the engine. But this is not the end. It is worth examining the inner surface of the oil filler cap. The presence of traces of a dirty yellow foamed emulsion on it is a very alarming symptom indicating that antifreeze is leaking into the oil. After removing the cap of the expansion tank or radiator, examine the antifreeze. Warning: to avoid injury, this must be done on a cooled engine! An oil film on the surface of the antifreeze, as well as foamed motor oil, are harbingers of urgent engine repair.
Well, that's probably all. We examined the "patient" completely, literally from the tip of the nose to the tail. And during the examination we used not expensive equipment, inaccessible to most car enthusiasts, but what is given to us by nature: sight, hearing, smell and, of course, the mysterious "gray matter".
An oily ring-shaped belt 6-8 mm wide on the outer surface of the car exhaust pipe ("mourning ring") is a consequence of increased oil consumption. A major engine overhaul is inevitable.
Black smoke
Sign of incomplete combustion of fuel. The fuel system prepares a very rich mixture and needs adjustment.
Smoke of blue (purple) shades
Sign of increased oil consumption. The engine requires replacement of oil seals or repair of the cylinder-piston group.
Thick white smoke
Sign of a burnt out cylinder head gasket. Coolant enters the combustion chamber.
Smoke with the smell of exhaust gases from the removed crankcase ventilation system pipe (breather) of the engine.
A sign of exhaust gas breakthrough into the oil pan due to increased clearances in the cylinder-piston group.