* Blown Head Gasket: This is the most common and serious cause. A blown head gasket allows combustion gases to enter the crankcase, significantly increasing pressure. This pressure forces oil out any available opening, including the dipstick tube. You'd likely also see other symptoms like white smoke from the exhaust, coolant loss, and milky oil.
* Cracked Engine Block or Cylinder Head: Similar to a blown head gasket, a crack in the engine block or cylinder head allows combustion gases to leak into the crankcase. This results in the same symptoms as a blown head gasket.
* PCV (Positive Crankcase Ventilation) System Failure: The PCV system is designed to vent crankcase gases. If it's clogged or malfunctioning (failed valve, blocked hoses), pressure builds up. This is less likely to cause *violent* oil expulsion like a head gasket failure, but can still lead to some oil loss through the dipstick.
* Ruptured Piston Ring(s): Severe piston ring wear or damage allows combustion gases to bypass the rings and enter the crankcase. This will create excessive pressure and likely cause significant engine damage. You'd likely hear other issues with the engine running as well.
Less likely, but still possible causes:
* Blocked Crankcase Breather: Similar to a PCV problem, a blocked breather prevents pressure release.
* Extremely High Engine Oil Level: While unlikely to cause expulsion through the dipstick, an excessively high oil level can increase pressure, particularly if the engine is running hot.
What to do:
Do NOT continue driving the vehicle. Driving with excessive crankcase pressure can cause serious and irreversible engine damage. The problem needs immediate attention. Have the engine inspected by a qualified mechanic as soon as possible to diagnose and repair the root cause. The diagnosis will likely involve a compression test and potentially a leak-down test to determine the extent of the damage.
