air puffs out of valve cover if oil cap is removed? 01 prizm

[dizwiz24]

Anyone else's car puff air out the valve cover - if the oil cap is removed while the engine is running?

I find this really odd, but likely normal - as my wife's sisters 07 matrix (with 12 k miles) does the same thing. As a sidenote, I replaced the engine due to oil consumption, with an engine from a wrecked 07 corolla 2 summers ago.

On other cars I have(chevy v8), if the valve covers are puffing air -out the oil fill cap, that is a sign of serious piston ring or valve damage.

Does your car do the same thing? At first I thought I had a clogged pcv, but this must be normal since wife's sisters car does this also.

[Downhillzze110]

its norrmal... its called crankcase vapors. and removing your oil cap with the engine running is a called a vacuum leak. not to mention a big mess.
all cars will have SOME crankcase vapors (Blow by gasses) because it is physically impossible for piston rings to seal 100 percent. now that being said if, in addition to puffs of air, large globs of oil come out of the oil filler hole THEN you may have an issue.

[Crowbar911]

I believe that air is caught by the PCV valve and sent back though the intake system to be burnt again is it not?

[Downhillzze110]

normally, crowbar, yes it is. but if you remove your oil filler cap; which has an O-ring on it for a reason, you create a bigger and more convenient release for your crankcase vapor. this is a vacuum leak and your car will run funny from it. not to mention you'll be polluting massively. in short, there's a reason why every book says to check and add oil with the engine off, that and the whole 'your dipstick reading will be WAY off'

[sapoverde]

Great info, downhill. I just did this on a car I'm think of buying and I didn't know what to make of it. Can you define globs? I removed the cap, vapor came out plus oil was spraying everywhere; small drops of oil though. Also, someone told me that vapor is a sign of worn o-rings. Thoughts?