If your vehicle is showing blue or gray smoke from the exhaust, especially under heavy acceleration or startup, here are the most likely causes and the parts you'll need to fix each one.
A stuck or clogged Positive Crankcase Ventilation (PCV) valve can cause crankcase pressure to build up, forcing engine oil into the intake manifold where it is burned during combustion.
Valve stem seals prevent oil in the cylinder head from leaking into the combustion chamber. When they harden or wear out, oil drips down into the cylinders while the engine is off, causing a noticeable puff of blue smoke on startup.
Adding too much engine oil can cause the crankshaft to whip the oil into a foam, increasing crankcase pressure and pushing excess oil through the PCV system into the intake to be burned.
Piston rings are designed to scrape oil off the cylinder walls. If they are worn or stuck, oil bypasses them into the combustion chamber and burns, typically causing continuous blue smoke under heavy acceleration.
On turbocharged vehicles, worn internal turbo seals can leak oil directly into the intake tract or exhaust system. This oil burns off under boost or heavy acceleration.