Oil filler Vacuum

[Wausau 911]

I know I read somewhere that with the car started and you remove the oil filler cap it is difficult (a little) to do as the pressure wants to such the cap on. Just cant recall if this is normal or indicative of something no so good??

[Ahsai]

It's normal if it's just a slight suction. Healthy crankcase vacuum reading is around 5" of H2O.

[bBunny]

If you experience major pressure sucking in, it usually means you AOS ( air, oil separator ) is on the way out ( indicated by volumes of white smoke blasting out of both tail pipes), You are not hurting anything at this point except the environment . The part(s) are cheap- $150+. The removal and subsequent new install is a pain. 5 hour labor probably more depending on what else you find once you're up in there.

[JFP in PA]

You are not hurting anything at this point except the environment .

I would not be quite that blasé about a failing AOS; when they start to fail, they can cause the engine to inhale a big slug of oil under certain conditions, which would lead to the hydraulic locking of one or more cylinders and the total destruction of the engine.

When you find an AOS going south, do not be driving the car around, get it fixed..............

[wvicary]

You are not hurting anything at this point except the environment .

I would not be quite that blasé about a failing AOS; when they start to fail, they can cause the engine to inhale a big slug of oil under certain conditions, which would lead to the hydraulic locking of one or more cylinders and the total destruction of the engine.

When you find an AOS going south, do not be driving the car around, get it fixed..............

Plus possible long term damage to catalytic convertors.

[Wausau 911]

Thx for all replies, not sure how to evaluate "major suckin". It wasn't difficult to remove the filler cap, just a bit harder to twist off.

Any other ways to determine AOS if going south on me?

[Ahsai]

You can use a digital manometer http://www.amazon.com/gp/aw/d/B005FU5HFI

Or make your own "U" shape hose version by drilling a hole in a spare oil cap, connect about 5' clear rubber hose to it, and put some engine oil in the hose. A 6" oil reading at idle is good since oil is lighter than water. http://forums.rennlist.com/rennforums/996-forum/738090-measured-my-crankcase-vacuum-6-water.html

Logray has an elegant setup here if you search his posts.

Edited June 9, 2013 by Ahsai

[Ahsai]

Another indication of margianl AOS is oil sweating and dirt accumulated at the bottom outside of the throttle body due to excessive oil collected via the AOS hose from AOS to intake.

[logray]

Here is the slack tube method...

http://www.renntech.org/forums/tutorials/article/255-an-inexpensive-way-to-test-for-a-bad-aos/