Excessive oil blowby?

[rigby]

I recently picked up a '92 GSX to use as a daily driver while building up my other car. Anyway, after removing the valve cover oil breather line and replacing it with a 'catch can' (really just a fram G2 filter), I've noticed that I'm losing a *lot* of oil through there even just under normal cruise conditions.

What makes this strange to me is that I did the same thing on my primary DSM (a '93 Talon AWD) and saw very little oil through there.

What's your experience here? Was the '93 abnormal, or is something wrong with the '92?

 

[Run-GSX]

I'm sure the '92 has higher miles , and was probably abused a little more than the '93. Probably more blow-by on the '92.

Otherwise , maybe your PCV valve has gone bad.

 

[rigby]

Actually, the '92 has far fewer miles on it, and the compression is about the same on both.

I pulled out the PCV valve and tested it. Definitely opens in the one direction, mostly closes off in the other. Not sure how much back leakage is normal on them though. Cheap enough I'll probably just replace it and see if it changes the behavior.

Another thought was to try another valve cover and see if that changes anything.

 

[Run-GSX]

You must be a Co.DSM member......me too

The PCV is supposed to only be open to vacuum.
Its supposed to close under boost , otherwise you get the problem you have........

It unlikley the valvecover is bad.....otherwise it would leak.....right?

 

[rigby]

Originally posted by Run-GSX
You must be a Co.DSM member......me too

Yup!

The PCV is supposed to only be open to vacuum.
Its supposed to close under boost , otherwise you get the problem you have...

Understood. What I was saying is that it doesn't close 'air tight' but pretty close.

It unlikleIt unlikley the valvecover is bad.....otherwise it would leak.....right?

Leak? No, I guess I was thinking that the internal vent passages might have deteriorated thus allowing more oil through the breather. I've got a couple spares, and I noticed that there's quite a restriction when you try to suck air through the breather normally. Dunno, just a thought.

 

[steve]

Originally posted by rigby
I pulled out the PCV valve and tested it. Definitely opens in the one direction, mostly closes off in the other. Not sure how much back leakage is normal on them though.

You found the problem. The PVC valve MUST seal when pressure is applied to the barbed end. It must open when pressure is applied to the threaded end. The only PVC valves I've found that meet the requirements brand new are the OEM from the dealer. Expect about 15 - 30k lifetime before needing to be replaced because it no longer seals manifold pressure. Every aftermarket PVC I've tested failed out of the box. I don't even bother anymore, I just buy OEM and I never have a problem with my dipstick popping up even with the original 12 year old seal.

Steve