924Board.org

[Fasteddie313]

While trying to troubleshoot my oil pressure gauge reading dangerously low I checked the cam oiling (witch seems fine) and found some spooky blowby..

So I checked the compression, TB wide open and about 6 cranks (edit: 6 compression strokes) each and I get...

1-126
2-120
3-121
4-125

cold engine, only ran for 2 minutes to back it up, no oil added to cyls, fuel pump off.. Plugs looked great, no sign of oil..

Witch is a little confusing because I thought S1 931 CR was 7.5:1 and 7.5 X 14.5 = 108.75 but maybe I don't fully understand the concept, or a PO did something interesting in there.. BTW its a proto tester so I believe it to be accurate..

So as for the blowby could it be exhaust valve seals? Or nothing to worry about? You can feel it about a foot away from the oil cap, not so much blow more like air reverberation, smells like exhaust.

But all this chase is from my indicated oil pressure..
20-50 full synth + zinc additive..

Start - 5.5 bar idle
Hot idle the light is on, blip throttle and it goes away..
Hot @ 2K rpm about 2 bar and doesn't seem to rise like it should from there, it gets about 3 bar at almost 5K rpm hot.

Hot means temp gauge at 1/4, maybe just a touch over..

I've been thinking its the gauge/wiring/grounding whatever because if I turn on any accessories like the lights or heater both the oil press and engine temp gauges read lower.

The engine runs great, starts great (any temp), idles great, boosts great, no scary noises.. IDK..

What do you guys think?
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80 Turbo - Slightly Modified

[emoore924]

IIRC the oil pressure spec is measured at a certain temp and RPM.

I'm making this up: Like the pressure should be 5 bar at 5k RPM and 100c.

It isn't unheard of for the light to flicker when the engine is hot and at idle. However, this could be early signs of main bearings that are headed south or a oil pressure control valve that's checked out.

Hopefully someone can check in with the actual spec...

[jason c]

931 spec= Oil pressure (at 5000 rpm)Up to approximately 6 bar (85 psi) at 80° to 100°C (176° to 212°F)
924 spec= System oil pressure (at 2,000 RPM)5 to 7 bar (71 to 100 psi) at 80° to 100°C (176° to 212°F)

Engine compression/ wear limit
Bar 8 to 11/ 6
Psi 114 to 156/ 85
Maximum allowable pressure difference between individual cylinders
Bar 3
Psi 43


Blow by can't come from valve stem seals, the valves would have to be leaking to get pressure to the seal. The seals function is to keep oil from entering the combustion chamber from between the valve stem & guide from top to bottom. The seals are not designed to hold pressure anyway, especially from the bottom up.

[brian19600]

From my Porsche owners manual:
"At idle speed, with the engine oil hot, it is permissible for the red warning light to light up - this does not indicate any loss of engine reliability."
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78 924

[Fasteddie313]

I have now noticed that my oil pressure gauge dips about 10% when I apply more throttle..

Like if I'm cruising steady in 4th the oil pressure dips a bit when I step on it to accelerate..

That mean anything?
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80 Turbo - Slightly Modified

[SlayerSST]

Just drive it until the engine blows.