Blue or grey smoke from the exhaust
The appearance of blue or grey smoke from the exhaust pipe indicates that engine oil is entering the engine cylinders and burning. This is a common problem that is accompanied by a constant decrease in oil level on the dipstick and requires immediate attention.
Likely causes — most common first
Worn valve stem seals
The rubber seals lose their elasticity over time and due to high temperatures, causing oil to leak down the valves directly into the combustion chamber. This is often noticeable as smoke immediately after starting the engine or after engine braking.
Worn piston rings
The metal rings on the pistons wear out or become clogged with carbon deposits, losing their ability to scrape excess oil off the cylinder walls. As a result, oil constantly enters the fire during engine operation.
Turbocharger problem
If your car has a turbocharger, wear on its internal seals can cause oil to leak into the intake manifold. From there, it is sucked in by the engine and burns, creating thick smoke.
Clogged crankcase ventilation
When the recirculation valve or ventilation tubes become clogged with combustion products, excessive pressure builds up in the engine. This pressure literally pushes oil through the seals into the exhaust system or intake.
