M3 rear main seal

[Suzy <suzym3@xxxxxxxxxxxxx>]

Several people have asked me what the oil filler cap has to do with the
rear main seal leaking.
I'm sure I will not do a very good job of explaining it but I will try.
As I understand it when you have a vacuum leak (as in the rear main
seal) the motor is trying to suck air through the leaking seal.  This is

what causes the squealing or whistling noise. When you remove the oil
filler cap the motor takes in air from the hole left by removing the
cap.  Therefore the motor isn't trying as hard to pull in air from the
leaking seal.  The squealing noise is then reduced or disappears.  When
you replace the cap again, the motor starts sucking air through the
vacuum leak again causing the noise to come back.  Don't know if this
makes sense, but it is the best I know how to explain it.

Suzy

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