oil gauge

[DSR]

this might be a stupid question but I searche the forum and did not see it discussed so I apologize in advance....

my oil gage (the one that is on the same dial as the fuel level) does not seem to move. It is always on the red. What is the normal level. FYI I have an 83 911sc ROW.

thanks

[Joe Bob]

Check and see if it is connected, check and see if it has power.....and obviously check and see how much oil you have on the dipstick.......

[schumicat]

normal level with engine idling (950 rpm) and oil warm (around 15-20 minutes driving in normal ambient temperatures) is about halfway. check the dipstick under same conditions to confirm it agrees (should also be about midway between marks - you don't want it at top mark).

[Grady Clay]

DSR,

The oil level gauge just reads the top few quarts (liters) of oil in the oil tank.
It should roughly mirror the level between the two marks on the dipstick (perhaps a bit wider).

Keep in mind that the oil level can only be correctly measured when the oil is hot, the engine is at idle and the car is on level ground.
The dipstick is the definitive measurement.
The gauge is only an in-car indicator.

When the oil is cold or you rev the engine, the level in the tank goes down due to more oil ‘in process’ inside the engine.
With the oil hot, the scavenge pump can refill the tank higher due to the hot oil flowing back to the bottom of the engine faster.
With the engine at idle for a bit, there is less oil inside the engine due to the slow turning pressure pump pulling less oil from the tank. The larger capacity scavenge pump refills the tank.

When everything is operating correctly, the gauge is a good indicator at a stop light when the engine is hot.



The oil pressure gauge is measuring the critical oil pressure inside the engine.
The pressure is roughly related to engine rpm (~1 bar, 15 psi per 1000 rpm) until it reaches full pressure (~60 psi, ~4 bar) where the pressure is limited by a pressure regulating valve.
The rpm at which the oil pressure reaches the limiting regulator valve pressure is temperature dependent.
With cold oil, the limit is reached at a low rpm.
When cold, the oil pressure will rise noticebly above the limiting pressure due to the restriction of the valve and associated passages.
(This is one of the reasons to not run your engine to redline when cold.)

With very hot oil, the rpm may be close to redline before reaching the limited pressure.
With very hot oil, the oil pressure reads very low at idle.
It is so low that the low oil pressure warning light would come on.
Porsche solved this issue by installing a lower pressure low oil pressure warning light switch.
(This is the reason for adequate oil coolers and engine cooling fan.)

All of this is also dependent on the weight of the engine oil (SAE30, 10W40, etc.) and the type (dino, synthetic, blend) of oil.

EDIT
Occasionally a 911 will have an incorrect (or modified) dipstick.
It is useful to compare dipsticks with other similar model 911s when you have the chance.
It would be useful to have a ‘dipstick measurement’ thread with pictures, measurements and part numbers.

Best,
Grady

[4sd911]

On my car the sending unit float in the tank will hang up on the dipstick holding it down. I remove the stick and leave it in a zip lock bag in the glove box or the door pocket.

[DSR]

thanks... will check when I get home ..I assume i have power as the fuel gauge is working.

[CaptainCalf]

If it's like mine on a 1987 930 the leads are separate from your fuel tank guage and here's what it looks like. It has 2 leads on it that you can access in the passenger side wheel well between the fender and the oil tank.