peteski

I have 2006 xB automatic with about 130k miles. Runs fine. I admit that I feel silly that I have never done in the 12 years of owning this car, but I have never removed the oil fill cap while the engine was idling. I just did that last week and there was air movement at the oil fill opening. But it is not just all sucking or all blowing air. It seems to alternate very fast between sucking and blowing. It is not a very strong effect, but it is is audible, and can be felt by placing my hand over the opening. I held a piece of paper towel over the opening and it didn't get sucked in or blown off - it was sitting over the opening vibrating. It seems that the suction pulses were slightly stronger than pressure pulses, because the paper towel was slightly stuck to the opening.

Can someone tell me if that is normal (or do that to their car and tell me what yours does)?

I have worked on older cars (American V8 engines) with PCV systems and in those the PCV valve was getting suction from the intake manifold, so if you took the PCV valve out of the rocker cover you could feel the suction on the PCV valve's intake port. Bit if the valve was installed in the rocker cover and I would remove the oil fill cap on the other rocker cover, there would not be much air movement at that opening (either suction or pressure). That is why I'm puzzled with what I'm seeing in my xB.

jct

it's normal

RichBinAZ

All quite normal. The pistons going up and down move the air from the bottom of one to one next to it.
It is actually a power loss in the engine (pumping loss) Theoretically, if you ran the sump at reduced pressure or near a vacuum, the engine would put out more HP - but nothing comes for free and there are issues with doing that. So nobody does that, yet.

peteski

Thanks guys!
Funny how I don't notice this in the V8 engine of my Caddy. Maybe with the some piston moving up while another is moving down the net air volume in the crankcase doesn't change?