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kidporsche · Posted: Wed Dec 01, 2004 12:05 pm Post subject: Oil pressure help

When I start my car, the oil pressure gauge reads ~5-6 bar (between idle and 4000rpm). After about 5 mins driving, the reading drops to 2 bar and 1 bar at idle. I have tried replacing the cam oiler elbow and the pressure relief piston and spring and different brands and weight oils. Changing the oil affected the numbers by 1 or 2 bar, but the trend is the same. What should I do next? New oil pump? I should note that I don't completly trust the gauge reading, but the oil light has been flashing on and that scares me.

Thanks,
Chris
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1981 924 - RoW (Australian) spec

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

Its kinda typical.
Check your volts when this happens.
It could also be a timing issue.
Synth oil should help.
Oil cooler.
Tweak your rpms at idle up a hair after warm up.(+50)
Make sure they are still in specs.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

What weight of motor oil are you using?

Seems like everyone is trying the stupid light -W20 and 5W-30 which are too thin for the 924 engine.

Use a good 20W-50.

5-6 Bar when the engine is started is normal. The pressure dropping when the engine warms up is also normal. A good rule of thumb is 1-2 bar at idle with the engine hot, and add 1 Bar for each 1K of rpm when off idle.

kidporsche · Posted: Thu Dec 02, 2004 11:23 am Post subject:

Have tried 10W-30 to 25W-65. The thing is that the gauge does not go up more than 1 bar with rpm. I've also had the light come on a couple of times on corners (I was going fairly gently at the time, too).
_________________
Chris
1981 924 - RoW (Australian) spec

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

May be you need to drop the oil pan and check the oil pickup.

Could be that gunk is being picked up while the engine is running that blocks the oil pickup. The gunk could be falling back to the bottom of the pan, to be picked up again when the engine is restarted.

Low oil pressure can also be a sign of a defective/worn oil pump (not highly likely), or worn-out bearings.

Paul · Posted: Thu Dec 02, 2004 2:48 pm Post subject:

While the oil pan is off, I'd check the rod and main bearings, both can be replaced without pulling the motor as long as the journals are within specs.

kidporsche · Posted: Thu Dec 02, 2004 4:48 pm Post subject:

I pulled the pan about 12-18 months ago, all seemed well. I have to say I'd be surprised and pretty worried if sufficient gunk had built up in that time to block the pickup.
Why does bearing wear affect oil pressure?
_________________
Chris
1981 924 - RoW (Australian) spec

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Bearing condition affects oil pressure because oil is fed directly to the bearings by way of passages through the engine block from the oil pump. Tight tolerances between the bearings and the journals, means less space for oil to escape out of, and higher oil pressure. When the bearings wear, clearances open up and there is more space for the oil to escape between the bearing and the camshaft, or crankshaft journal. More oil escapes, and you get lower oil pressure throughout the system.

kidporsche · Posted: Sat Dec 04, 2004 6:59 pm Post subject:

How hard is it to replace the conrod and main brgs in-situ? How long would it roughly take?

Cheers,
_________________
Chris
1981 924 - RoW (Australian) spec

Paul · Posted: Sun Dec 05, 2004 3:18 am Post subject:

Once the oil pan is off, the connecting rod bearings are very easy to replace by simply unbolting the rod caps and pushing the rod up.

The mains are a little more difficult since you have to rotate the top bearing into place. (I'm trying to remember if I've ever done this on a 924, I've done it on other motors) I have replaced several sets of 924 main bearings with the motor in a stand and the crank out.

I usually spend more time checking the clearances (with plastigauge, etc) then it takes to replace the bearings themselves.

With the pan already off and not counting the time to put the pan back on nor the time it takes to check the clearances, I could do the rod bearings in less than 20 minutes and the mains in less than an hour.