astvic

Gents,

I have now bin driving in my "new" car (S4 aut. 1990) for 4 weeks
So of course things pops up now and then. One particular thing is this ?
Please advice me on the following

When I start the engine (cold) my oil-pressure gauge more or less exceeds the 5 bars.
When the engine is varm (89C / 192F) then suddenly the gauge begins to work, but can still exceed 5 bars (idle at 2-3 bars) .

BUT on top of that if !!!!!!!! If I accelerate I can see the oil-pressure increasing (=OK), but when I remove my foot from the gas pedal, while driving, I get this strange loud resonance sound from the back (sound like the exhuast and at a low frequency). when the sound is present I have noticed that the oil-pressure is constant.
But when the "sound" disappears (like on / off) the oil-pressure immediately decreases to, in most cases, 2-3 bars (idle).
This is of course, because my foot is away from the gas pedal

Question !
Can e.g. the exhaust system influent the oil-pressure or is it a coincidence ? or maybe several things at the same time.

ASTVIC

WallyP

Normal oil pressure on the 928 is 2-3 bar at idle, 5 bar at speed.

One possible cause for your noise is an exhaust that is hitting the body.

Check the motor mounts - it is fully normal for 18-year-old mounts to have collapsed.

AO

You oil pressure sounds good to me, but I think you need to track down this sound you're getting.

Can you tell me what the RPMs are when you hear the sound? My guess is that it is RPM related.

Jim bailey - 928 International

When cold the engine makes more than 5 bar so the gauge IS WORKING it is just at the maximum reading. As the engine warms up the oil gets thin and at low engine speed low oil pump speed the gauge shows the 2 bar or so. Since the oil pump speed is determined by the engine speed what you do with the gas pedal DOES change the oil pressure.

astvic

Thank you for the feedback

So I think I can conclude that the oil pressure is OK !

Regarding the "sound" and impact on the oil pressure gauge, let me be a little bit more precise !

This is the scenario :

I accelerate the oil pressure increases (up to 5 bar)
I remove my foot from the gas pedal (car begins to loose speed)
The "sound" begins and the oil pressure begins to decrease
The "sound" suddenly dissapears and the oil pressure gauge (needle) stops for right after to increase a little bit (0,25 bars maybe)

It looks like that the "sound" has impact on the oil pressure or at least the gauge ????????????
If I begin accellerate while the "sound" is present, the "sound" stops immidiately !

I have not expirenced that it's RPM or velocity depended. It can happen at all velocities and all RPM's.

ASTVIC