Rhythmic humming at startup - Oil trap related?

[mieses]

The B6324S engine is naturally aspirated. This engine is used in both the 2008 XC70 3.2L and 2007 XC90 3.2L. I don't think it has secondary air injection. https://en.wikipedia.org/wiki/Volvo_SI6_engine#B6324S

The rhythmic hum at idle definitely comes from the diaphragm which I will probably replace again. Why would the diaphragm fail after just a few weeks?

There's a good overview of the engine at https://clubvolvo.ru/threads/prinimajte ... st-2631982 and https://www.drive2.ru/l/501335521897742599/ (in Russian, use Google Translate).

[SuperHerman]

If it doesn't have a secondary air pump then that can be excluded.

Original poster has a PCV related issue - blockage some where in the system. It is not in the parts that were replaced. New diaphragm is failing because of the excess pressure - oil leak is also related. The pressure is finding the seals the easiest way out - hence the new oil leak. Usually solving the pressure issue will stop the leaks from the seals.

RickHaleParker posted a picture of the system - those paths have to be examined to make sure they are not restricted.

[blaudp79]

Have you ever figured out what caused this? I have the same problem and I'm wondering whether I should chase the oil separator channels with those oil gallery brushes.

[Wumbo]

My theory is that it's related to the vacuum pump. The seals tend to go when the breather box has been having problems. I have a small oil leak at the vacuum pump, and when I pump my brake pedal a couple times, the humming stops. I'm going to change the seals in the pump and see if it makes a difference. I'll report back with how it goes - just thought I'd put the idea out there in case somebody else is troubleshooting this problem at the same time as me.

[PecanGuy]

My car has exactly the same phenomenon of rhythmic humming after I replaced the oil trap with a Volvo one. Has anyone figured it out? Thank you for helping.