Blue or gray smoke coming from an exhaust pipe indicates either an oil leak or piston wear. Typically, oil leaks pass the seals and get into the engine cylinder. From there, they come into contact with gasoline and burns, producing blue smoke. When oil leaks into the cylinder, it produces rough idle, misfires and could affect the spark plugs, according to CarsDirect.
If your vehicle emits blue smoke from the exhaust pipe, it should be thoroughly checked for oil leaks as a first line of defense. If all is well, blue smoke could indicate wear and tear on the engine seals. Your mechanic should check the piston rings, valve seals and valve guides, according to About.com. The positive crankcase ventilation system should be evaluated for damage and loss of compression. Those seals and valves may need replacement. Have your mechanic evaluate the intake manifold and the head gasket.
Other symptoms of an oil leak include a loss of power and a decrease of oil volume. Oil lubricates the engine and keeps friction parts from overheating and seizing. Your vehicle cannot operate without sufficient oil levels and pressure. If you suspect that your vehicle is leaking oil, as indicated by blue smoke, take it to a certified mechanic.