PCV Valve: How do you tell when it's bad, How often to change?
 

I have been reading all the threads regarding oil leaks, because when I was in changing the serpentine belt recently, I noticed what looks like an active leak at the heat exchanger/oil cooler on my '03 MCS. I also recently changed my oil and filter, so at first I thought it was spillage from the filter change, then after cleaning up worried that it might be that the filter itself was leaking. I did change the o-ring when I changed the filter. I re-checked the torque on the filter housing and it seems fine. I'm going to have to do something about the leak for a number of reasons, not the least of which is because I see some oil on my tie rod boot and that simply won't do. I suppose the place to start is to pull the filter and confirm that the o-ring is properly seated, but I suspect the oil cooler o-rings or filter housing gasket is to blame.

Anyway, in one of the threads, I think ZippyNH mentions that oil leaks can be exacerbated by PCV Valves going bad. And others chimed in with +1. I have gone through my Bentley and it really pays faint attention to the PCV Valve. Unless I missed it, there is no mention of a schedule for prophylactic replacement of the PCV Valve. Neither is there a diagnosis protocol for finding a bad PCV valve. I know the part is not too expensive, but I would like to 1) understand the theory of operation more than I do (even after reading the Bentley), 2) understand the failure mechanism, 3) have some fact-based insight into what a proper maintenance schedule for this part is.

Any of you knowledgeable mechanics got a moment to bring me up to speed?

Just pull the PCV out and shake it. If the little check ball is rattling, it's very likely ok.

You can use carb or brake cleaner to flush it out as well. It may be a little damp with oil and that is OK too.

If you shake it and you hear nothing, change it.

+1
That's the test....or just spend the $20 cause it old..they are not lifetime parts.....
Premise is if it sticks, or does not move freely, the crankcase can become partially presusrised...pushing out out of areas that should not have psi... Like the oil pan gasket and valve cover. Very basic under hood check....about as basic as a fluid check...but some of the basic stuff gets overlooked, and it costs big $$.

As to WHY a pcv...it is an early, basic emissions part...
Blow by from the motor was once vented in a tube to the ground in what was called a "breather"... But they dripped oil...and had unburnt hydrocarbons from the fuel...so it was routed back to the intake (more it less)...and a bit of valving was needed to make it work right...if the valve sticks either way...things don't function right.

Ok, that helps a bit. I had also read (somewhere in cyberspace that I can't find at the moment) that the shake test was only a good diagnostic test for early PCV valves, but not modern ones. That was the basis for my question, but if that is the technique the MINI cognoscenti are using succesfully, so be it.

As you say, the PCVs are not too spendy so maybe at 100kmiles a replacement is warranted. But the list of things to do at 100k is adding up to a sizable sum of cash, at least for those of us with little to no disposable income!

do the shake test. dont waste your money (about $30) like me.
shake it, or blow through it (in / out). should go one way, not the other. if it does, its fine. your oil leak is elsewhere.

After you've cleaned it, you should be able to blow through it from one way and not the other. The cleaning is just to save you from getting a mouthful of used engine oil. BTW, the shake test does work on Gen 1 PCV valves - they clearly sound like they have a metal ball in there.

Certified (certifiable?) procedure:

1) Clean with degreaser/brake cleaner, let dry.
2) Open good beer. No "light" swill.
3) Blow through PCV valve to test. Reverse and repeat.
4) Drink beer to remove taste of oil and brake cleaner
5) Congratulate yourself on saving $20 (less the cost of a beer).

That's a pretty good rough draft of a procedure. I think you left out the part where steps 2 and 4 get repeated.