Strange air leak

[Jon124]

The other day I was inspecting my FI Spider for air leaks and I noticed something that I haven't seen mentioned in the forum before. I was using ether around all connections and hoses and the intake to see if the RPM changed at all, and it looked like everything was good and sealed. When I was on the intake side of the car I could hear a very faint air rushing sound, and I determined it to be coming from the dipstick. When i pulled the dipstick out the RPM dropped quite a bit, same thing happened when removing the oil cap. I was just curious if anybody had seen this before, it might be a good check when diagnosing FI air leaks.

The vacuum in the crank case is due to the large vent hose that goes from the block to the intake. Unlike PCV systems the Fiat does not have a crankcase breather, so there is not constant air circulating through the block. The vent hose applies vacuum to the block to extract blowby gasses, so any seal leaks on the crankcase can allow un-metered air to enter the intake.