Black smoke is the most common type of smoke emitted from diesel engines, which indicates poor or incomplete combustion of fuel. Some of its causes are:

• Incorrect timing or valve clearance
• Dirty or worn out injectors
• Over fuelling or poor quality fuel
• Excessive carbon build up in combustion and exhaust spaces

Blue smoke is an indication of oil being burnt. Some of the reasons for oil to enter combustion chamber are:

• Wearing in some parts of power assemblies like cylinders or piston rings
• Worn out valve guides or seals
• Incorrect grade of oil
• Piston ring sticking

White smoke is emitted when raw diesel comes out through the exhaust completely intact and unburned. Some causes are:

• Faulty or damaged injectors
• Incorrect injection time resulting from possibly worn timing gear or damaged crankshaft
• Low cylinder compression caused by leaking valves, cylinder glaze, or cylinder wear Sometimes white smoke is also created due to water entering combustion spaces.