bokenoet

I'm building a 944 (early '85) as a Chumpcar/trackday car, and I've run into a problem after rebuilding the engine. I just fired up the engine for the first time, and the oil pressure hangs around 1 bar at idle, and only increases to 3 or 4 bar when I rev the engine.

I've tried switching out the OPR valve (both the 3-piece and the single piece version), re-torquing the crank bolt, and bleeding the air out of the cooler (I've installed the turbo oil cooler housing on the motor with an aftermarket heat exchanger). The oil pickup looked free of cracks when I installed it as well. None of these checks had any effect on the pressure reading or behavior.

My next step was going to be to replace the oil pressure sender, but if that fails I'm not sure what to check next.... Does anyone have any other suggestions?

Some more details on the motor rebuild:
-Rods/main bearings and all seals replaced
-The crank has been cross drilled
-Oil pan baffel and pickup shroud (similar to the Lindsay racing one)
-Turbo oil filter housing with aftermarket oil cooler

xsboost90

i think trying a different gauge/sender may help.

Butters944

Oil pressure sender is a very easy replacement. Got mine from napa for under 100 bucks, kinda pricey, but lifetime warranty.

odurandina

drive it til it blows up. motors are cheap.

Butters944

YOU JUST WANT HIM TO BLOW IT UP AND GET AN LS1!

xsboost90

great advise as always.

kev951

oil pressure sender is only 20 bucks online or wholesale, you can also make your own gage to thread in the same port and run the engine. did you rebuild your oil pump? did you change the seal on the pickup tube? 1 bar at idle when its cold?? no good my friend. something is a miss. how is the heat exchanger installed in conjunction with the turbo console? That's a first for me.

bokenoet

Ok so I've tried both a different sender and gauge, with identical results, though now it goes to 4 bar on idle and slowly moves down to 2 bar after a couple minutes at idle. It is still responsive to revs though, even a small throttle application will cause it to jump back to 4 bar.

However, I did find that I probably bought the wrong bearings, since my machinist took off 0.010'' when he polished the crank, and I just threw on a set of standard bearings back on. I assume that I'll need the 0.25mm sized up bearings, and that this extra clearance in the crank is what is messing with my oil pressure at low revs... I'd be afraid to run it for long now with the current bearings.....

xsboost90

buy some std bearings and i have a crank that is fresh that can drop right in.

car_slave

I think 2 bar at idle is okay. Check the Porsche specs for oil pressure. What grade oil are you using?

From Clark's - you should try to find the official numbers to verify.
The 944's oil pressure should run 4-5 bar at idle when the engine is cold. It will gradually decrease to 2-3 bar at idle as the engine oil warms to normal operating temperature. Once the oil is at normal operating temperature, the oil pressure should indicate around 4 bar at 5,000 rpm.

odurandina

running 4.5 bars with my 0w40/0w50 mix. further proof that my engine is indeed, doomed.

xsboost90

i dunno but my last two/three cars have had 4-5 bar cold at an idle, and 3.5 hot even during track days- maybe 3 at the least. Running 20w50.

car_slave

My 968 runs just above 2 bar idle hot with 0-40 syn My 944 is 3-3.5 (bouncing) bar hot idle with 10-40 reg. Porsche's min spec for a 968 is 3bar at 3k rpm. I've read of some turbo owners who get 1.5 bar hot at idle.

It looks like you've got a lot of time and cash put into this motor - maybe too much? Some say that worn main bearings can cause the fatal #2 rod bearing oil starvation problem. Sounds like you're closer to the min than max. I guess you did all the work so you'd have a reliable car in the end, so...

bokenoet

well, it is for a race car, and our first race (Chumpcar at Road Atlanta) is going to involve a 10 hour race on the first day.... So I'd rather not chance any oil pressure problems, especially after my team and I put the time and money into putting this car back together and taking it down there....

M758

Don't run it this way as the motor will spin a bearing sooner or later.

I never have the crank journals ground on my motors as it will open up the clearances too much. You can go with oversize bearings, but these cost more than finding a crank. Plus you have replace them and pay more again.