PCV/ Glove test failure 04 XC70

the65dartguy1 · Post by **the65dartguy1** » 08 May 2017, 10:44

I recently acquired an 04 XC70 and am going thru it, catching up on missed maintenance items. One of these is of course PCV. I bought the kit from FCP and did the job. Still fails glove test. I dropped the oil pan and did that job. Still fails glove test.
What am I missing here? car runs good otherwise, ( perhaps its idles a tad off. It has 172k on it)just want to get this taken care of.

Ideas?

zoli_m13 · Post by **zoli_m13** » 08 May 2017, 12:54

Don't worry - you are not alone!

2001 S60 Any preventive maintenance proposal? Topic is solved
Postby jbeebo » 05 May 2017, 20:35
It's near impossible to get perfectly balanced neutral pressure in a crankcase, so a slightly positive (for turbo engines) or negative (for N.A. engines) pressure is not unusual IMHO. Sounds like everything is working as it should.
Many engineers over many generations have struggled with this and continue to invent new ways, just check GM's new L5P diesel engine oil separator design (text, video).

Positive pressure could be coming from the rings as you mentioned, or from turbo blowby. Some amount of blowby is to be expected, even on a new turbo. Turbo seals are simultaneously simplistic and highly complex beasts. By design they have clearances to the ShaftWheel Assembly, and thus leak small amounts of air (bringing some oil along with it)./

Post by **vtl** » 08 May 2017, 13:04

Fails the test on idling engine or loaded above 2500 RPMs?

Post by **JRL** » 08 May 2017, 14:58

Did you include the (expensive) big tube?
If not you wasted your time and money!

Did you check the passages that go to the pan and were cleaned out properly?

Who wrote that above? Positive pressure? NO WAY

Post by **vtl** » 08 May 2017, 15:04

Agree no constant positive pressure should be in a normally functioning engine.

Post by **June** » 08 May 2017, 18:35

vtl wrote: ↑08 May 2017, 13:04 Fails the test on idling engine or loaded above 2500 RPMs?

I have to ask this question because I don't really understand these pcv systems. Okay on a turbo Volvo engine the vacuum comes from the intake manifold which is highest at idle, but once the turbo engages it puts positive pressure in the intake so where does the vacuum come from or does some of the boost pressure backtrack the pcv causing normal positive pressure in the crankcase during boost the return to negative pressure after boost or is the crankcase pressure supposed to stay negative even at WOT at maximum boost pressure? Does some sort of valve in the line to the intake prevent positive boost pressure from backtracking the system? I really have wondered reading so many posts about pcv not operating correctly on here exactly what is correct operating spec for turbo engines from idle without boost to with boost pressure and higher rpm? Thanks, June

zoli_m13 · Post by **zoli_m13** » 08 May 2017, 22:19

You are not alone, part #2:
viewtopic.php?f=9&t=69305#p438480

the65dartguy1 · Post by **the65dartguy1** » 09 May 2017, 04:58

The tests were run at idle... to the best of my knowledge that was how they were supposed to be carried out. It is also rather difficult to do by yourself in any of the electric throttle cars!
I did not replace the big tube, but did clean it out thoroughly. In my experience that has been sufficient.
Oil pan passages and those in the block leading to the pan were cleaned/clear.

Post by **vtl** » 09 May 2017, 08:14

June wrote: ↑08 May 2017, 18:35 I have to ask this question because I don't really understand these pcv systems. Okay on a turbo Volvo engine the vacuum comes from the intake manifold which is highest at idle, but once the turbo engages it puts positive pressure in the intake so where does the vacuum come from or does some of the boost pressure backtrack the pcv causing normal positive pressure in the crankcase during boost the return to negative pressure after boost or is the crankcase pressure supposed to stay negative even at WOT at maximum boost pressure? Does some sort of valve in the line to the intake prevent positive boost pressure from backtracking the system? I really have wondered reading so many posts about pcv not operating correctly on here exactly what is correct operating spec for turbo engines from idle without boost to with boost pressure and higher rpm? Thanks, June

Under load the vacuum is taken from fresh air pipe just in front of turbo via heated PTC nipple. Crankcase can have positive pressure for a short time when the system is switching vacuum source and there's a vacuum shortage due to inertia of the system.

Post by **vtl** » 09 May 2017, 09:17

Intake manifold's heated banjo bolt has a valve inside it, it shuts off backpressure from intake under boost. It gets dirty over years and needs to be replaced.

I did not replace it 4.5 years ago when was doing full PCV (somehow I got a wrong banjo bolt with FCP kit) and 4 years later my PCV broke. Old bolt looked fine back then, I cleaned it thoroughly, but apparently you have to replace EVERYTHING in PCV.