Possible causes are blown head gaskets, cracked heads cavitation, etc. Like going up a steep grade, being loaded heavy or during heavy acceleration. More black smoke can be observed when the vehicle is operated at higher altitudes because the air is thinner. A dirty air filter is also another cause of excessive black smoke. If black smoke is noticed while the engine is idling at low altitude or under normal driving conditions this condition should be diagnosed a.s.a.p. to prevent engine damage.
Blue smoke occurs when oil is entering the combustion chamber and is burning along with the fuel.
Blue smoke usual indicates a condition which should be corrected a.s.a.p. Blue smoke also smells like oil burning. Possible causes include valve seals or cracked piston rings.