What causes blue smoke while starting?

What could be the cause of blue smoke coming out of the exhaust when I crank my car?


Answer:
Blue smoke is the product of oil burning.
During cranking, an engine with one or more slightly worn oil control piston rings will burn the oil that was deposited on the cylinder walls at shut down. Also, a small amount of oil may leak past the piston rings when the engine is being cranked due to temperature-induced clearance and tolerance changes. This usually happens on higher-mileage engines with somewhat worn oil control piston rings.
After the engine warms up, heat causes tolerances to tighten and parts such as oil control rings to fit tighter in the cylinders thus preventing further oil leakage past the piston rings.
In engines having mildly worn rings, the tighter tolerances at running temperatures will often limit ongoing burning of oil.
Changing oil during the life of the engine as recommended by the manufacturer of today’s engines will often prevent this condition from developing.

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