* Increased crankcase pressure: The excess oil can't be properly contained and pressurized by the crankcase ventilation system. This can lead to leaks from seals and gaskets, forcing oil out past seals and potentially damaging them. It can also blow oil into the air intake system.
* Foam oil: The crankshaft can churn the excess oil, creating excessive foam. Foamy oil doesn't lubricate as effectively, leading to increased engine wear.
* Damage to seals: As mentioned above, excessive pressure can push oil past seals, leading to leaks and seal failure. The seals can also be damaged by the foamy oil.
* Damage to crankshaft: In severe cases, the churning of excessive oil can put extra strain on the crankshaft seals and bearings.
* Air intake contamination: Oil can be forced into the intake manifold, contaminating the air-fuel mixture and potentially leading to misfires, rough running, and damage to the catalytic converter or oxygen sensors.
* Damage to PCV valve: The Positive Crankcase Ventilation (PCV) system will struggle to manage the extra pressure and volume, potentially leading to its failure.
It's far better to be slightly under than over on oil. Always check your oil level using the dipstick after the engine has been off for at least 10-15 minutes to allow the oil to settle. Overfilling is less common, but can lead to serious and costly repairs. If you suspect you've overfilled your oil, you should drain some oil immediately.
