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      11-22-2015, 11:22 AM   #19
vespa
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Drives: 2011 335i
Join Date: Dec 2014
Location: Thousand Oaks

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The oil cap test absolutely confirms that the noise is coming from a main seal but it doesn't explain why. It's certainly possible that the seal is bad and the PCV system is fine.

The smoke test will absolutely confirm a bad PCV valve and is very simple to do. Lift off the decorative center engine cover and unclip the little decorative cover from the hose barb. Hold a burnt match or something very close to it and if smoke is continuously drawn in, the valve is unquestionably broken.

If the smoke test is inconclusive, the next step would be to replace the oil cap with one that can measure pressure, then confirm that idle pressure is around -0.55psi, particularly while the noise is present. If you're reading -1.0psi (or -1.5psi in my case), the PCV valve is absolutely broken. Otherwise, you just have a bad main seal. Front tends to make a chirping or squeaking sound, especially when hitting the brakes while the rear tends to be a louder more continuous squeal.

I added an oil cap/pressure test/rear main seal video to the first post.

Last edited by vespa; 11-22-2015 at 11:34 AM..
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