* Failed PCV valve: The PCV valve is crucial for venting crankcase pressure. A faulty or clogged valve prevents proper venting, causing pressure to build up in the crankcase. This pressure forces oil up past the piston rings and into the intake manifold, eventually exiting through the throttle body. This is a very common cause.
* Worn piston rings: Worn or damaged piston rings allow excessive blow-by (pressure from the combustion chamber leaking past the rings into the crankcase). This significantly increases crankcase pressure, leading to oil being forced into the intake.
* Worn valve stem seals: These seals prevent oil from leaking down the valve stems. If they're worn, oil can get into the combustion chamber and be forced back into the intake. While this oil wouldn't directly come *from* the crankcase, it still ends up in the intake and exits through the throttle body.
* Clogged crankcase ventilation system: The entire PCV system needs to work together. A blockage anywhere in the system (hoses, passages) can create excessive pressure leading to the same problem.
* High crankcase pressure due to other issues: This could stem from problems like a failing head gasket, a cracked block, or other issues that cause increased pressure within the engine. These are more severe problems.
It's crucial to diagnose the root cause immediately. Continuing to drive with oil blowing back into the intake can lead to:
* Engine damage: Oil in the combustion chamber can lead to misfires, excessive wear, and potentially catastrophic engine failure.
* Sensor damage: Oil can foul sensors in the intake manifold, leading to inaccurate readings and potentially more problems.
* Air/fuel mixture problems: Oil contaminating the intake air can affect the air/fuel mixture, leading to poor performance and potential damage.
Do not continue driving the vehicle. Have a qualified mechanic diagnose and repair the problem as soon as possible. Ignoring this issue can lead to significant and costly engine repairs.
