What causes vacuum that can be relieved by loosening the oil

mimic · Post by **mimic** » 30 Jun 2011, 09:03

What causes a vacuum that can be relieved by loosening the oil filler cap on a S40 T5?

Post by **FlyingVolvo** » 30 Jun 2011, 09:09

Are you saying that your oil filler cap sucks in air? If so, that's a good thing! Your car has a PCV (Positive Crankcase Ventilation) system that takes the high pressure blow-by from the engine and reroutes it into the intake to be burned.

After the car is warmed up, with your engine running, go under the hood and pull the oil dipstick. There should be no white smoke or pressure coming out. Instead, hold a light tissue or something and see if it wants to be sucked in. If it does, you have nothing to worry about. If it is blown out, then you've got a problem.

Post by **jimmy57** » 30 Jun 2011, 09:17

Lots of suction and sometimes with kazoo noise on the P1 5 cylinders is the crankcase pressure regulator device integrated on the oil filter housing has a ruptured diaphragm.
The diaphragm balances crankcase pressure with vacuum above it and should keep crankcase pressure to a VERY low pressure to a faint vacuum that would not be readily noticeable.
When the vacuum level is high enough to struggle against when removing the cap it is usually due to the diaphragm rupturing and connecting the vacuum side to the crankcase side directly.