When I open the oil filler cap, there is a vacuum. The engine is trying to suck the oil cap back.
Why?
Where does this vacuum come from?
In: 1
There is a valve, called the positive crankcase ventilation (pcv) valve. This valve pulls gasses out of the crankcase and into the engine to be burned. This is better than letting them loose into the air. It’s powered by engine vacuum, the same thing that draws air and fuel into the cylinders.
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