1990 740 Turbo Positive Crankcase Pressure

diegotheslinger · Post by **diegotheslinger** » 23 Jul 2019, 19:04

Hello all!

Been lurking on this site but am kinda stuck with my 740 Turbo right now. I've had pretty bad positive crankcase pressure for awhile, I can feel it coming out from oilcap when its off. Bit of smoke comes out when its warmed up too.

Car is at 250k, I tried at first just cleaning PCV box... Didn't really work. Got new one put that on and replaced couple hoses when I just did a headgasket replacement. (First one ever, took some time but learned alot.) Still no real improvement. I've had bad oil leaks for awhile now, seems to mostly be from oil cap and somewhere around turbo. (Tried two new caps, no change) Good amount of oil in Air Intake Hose.

Could this be blowback from block? Maybe some vacuum blockage somewhere?

I did a (dry?) compression test on it before replacing headgasket about 1000mi ago.
Cylinder 1 = 130psi = This one was scrubbed clean from coolant
Cylinder 2 = 140psi
Cylinder 3 = 145psi
Cylinder 4 = 150psi

Thanks for any tips, i'm self teaching myself mechanics so still don't know alot. Love the car tho and want to keep it on road but I need a reliable daily driver. Thanks.

lummert · Post by **lummert** » 25 Jul 2019, 07:30

On my 309K mile 1988 760 Turbo Wagon I mounted an open filter breather to the valve cover, installed a Toyota Supra Twin Turbo PCV valve between oil breather box and intake manifold vacuum port. I plugged the nipple on the turbo inlet hose. Works good at controlling crankcase pressure.

diegotheslinger · Post by **diegotheslinger** » 25 Jul 2019, 16:41

I think I'll try this out and see how it does. Maybe I can mount vent on oil cap, seeing as I have like 3 of them now.