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dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

On my 81 the oil pressure goes to 10 bar on cold start ups. As it warms up the pressure drops to 4 to 5 bar. At what pressure should the pressure relief valve open up? Is 10 bar too high?

Thanks in advance.

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

Lizard · Posted: Sun Mar 14, 2004 6:09 am Post subject:

I would have to say that is about right on startup, however once warm it should be around 1 bar not 4 or 5
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3 928s,

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Lizard,

Sorry, I should have been more specific. Cold idle is 10 bar. Warm idle is 2 bar. The highest when warm is 5+ bar at 3K+ rpms. I thought the pressure relief valve would stop pressure from getting too high even when cold.

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

Smoothie · Posted: Sun Mar 14, 2004 9:19 am Post subject:

10 bar does sound impressive. I've never seen any more than 7, possibly 8 when cold and at 4000+ rpm. They give specs for just about everything in the oil system it seems except for the opening pressure of the relief valve. Maybe it's stuck? If it's electrical, your grounds are toooo good.

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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Smoothie,

Is it possible that the cold spring on the valve would let it go that high? On my 928's the relief valve kicks in a 5 bar (max on gauge). Since the 931 has a 10 bar gauge, maybe it has a 10 bar relief valve??? Guess I'll pull the valve and check it. On my 80 NA (RIP) a PO had shimmed the spring trying to increase the pressure.

Thanks,

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

Smoothie · Posted: Sun Mar 14, 2004 10:54 am Post subject:

I don't know. That's way off the charts compared to what I get. I just went on a run to a store and on cold startup it read 6 bar at idle. Three miles and about 10 minutes later, back on the driveway again it was 3.5 bar at idle.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

numbbers · Posted: Sun Mar 14, 2004 12:32 pm Post subject:

Mine reads 8 bar at startup, and gets as low as 2 on really hot days. I think you are in the normal range.
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1980 924 Turbo

Paul · Posted: Sun Mar 14, 2004 1:31 pm Post subject:

The 931 factory shop manual states:

Oil pressure(only for SAE 20w 20 oils) at 176 degrees oil temp and 2000 rpms: 3 - 6 bar ( 43 - 85 psi).

Wear limit : 2.0 bar (28 psi)

Zuffen · Posted: Sat Mar 20, 2004 1:14 pm Post subject:

Hmmm I would swap the oil sender out first and see if it reads the same.

Also another trick is to T off the port and add a phsical gauge mounted in the engine bay, for diagnostic tuning.

I've had trouble with my car having low readings on bad electrical days.

The oil light will kick on at about 1.5 bar to let you know the pressure is too low.

As for a high reading, If they stick a 10 bar that means you could expect to operate up to the 10 bar, the question is if your over that.

What oil filter are you using? I've heard that you have to watch filters as there ate have some that restrict the flow excessively and even have built in pressure valves that can stick.
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Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Bob,

The oil pressure comes down as the engine reaches operating temps. It has done this with two different brands of oil filters, the last being an STP. I know not to use FRAM. I was thinking about swapping the relief valve from the 79 I have on the stand, but noticed that it has the later 944 (one piece type) installed.

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

Zuffen · Posted: Sat Mar 20, 2004 1:30 pm Post subject:

I remember a story of there being a good failure rate on a run of those oil pressure senders, usually leaking was the problem but what if it not calibrated after all these years of use?

I can tell you that you welcome to the valves I have on the spare motors in the garage if you want to test that end.
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Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Thanks Bob,

I'll add it to my shopping list.

Been driving the silver beast this week, so now I have a list of things to do on it.

Does it never end?

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black