911SC Oil pressure gauge

The oil pressure gauge constantly indicates "5" when the engine is at operating temperature and the rpm are anything above 2000-2500. As you exceed 2000rpm the needle flickers a bit and settles at 5. I changed the oil pressure switch(the one that sits above the engine, next to the fan)recently and this improved the reading when the engine is cold and for rpm below 2500.Is there a second sender unit somewhere? Does this indicate a faulty gauge?
I use synthetic oil.
Any ideas/comments are welcome. Thanks in advance

[This message has been edited by Renos (edited 11-12-2000).]

Hi Renos!

I had got some problems with the oil-pressure gauge too, and it turned out to be the instrument itself. First you should ask somebody to give You the ohm-line of a correct working switch. (In the 3,2 it should be 0-180 ohm - got the information some time ago, but I´m quite sure - depending on the reeves). Mine was working fine. Then I checked the cable. It should be nearly 0 ohm. And then I put of the instrument (carefully with a big screw driver towards the steering wheel). My instrument was constantly showing over 5 bar - needle at the end of the scale. The oil-tempreature-instrument is working with the same system, so I changed the cables - and the neede of the oil-tempreature moved depending on the reeves. So it was the instrument itself. In Germany we have VDO-specialists, who just are changing the broken parts. You can save some money on it.

Just try - its easy. And good luck

Regards

Tobias

The oil pressure sender sounds suspect ... as if it is going 'open' at higher pressure! The pressure switch is not related to gauge operation, it is just for a warning light!

You can test gauge and wiring operaztion with the engine not running, but with the ignition switch 'on' by removing the wire connector from the sender and temporarily connected to a 10K Ohm potentiometer wiperand with one side 'grounded with clip leads. You should be able to sweep the entire range of the gauge by moving the potentiometer wiper shaft.

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Warren Hall
1973 911S Targa

Warren, you're out of my league with all this talk about potentiometers. But I do remember that an open connection will 'peg' the meter. This means that unusually high readings could be the result of a simple bad connection.

I believe there is an oil pressure switch in the back of the engine, on top, but this does not affect the gauge. the gauge is fed by a sender on top of the right chain housing. If it reads normally in one range, and then off the scale at higher rpms, then my guess is the sender is bad. But I'd sure wiggle all related connections first.

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'83 SC

Super,

Actually, it might surprise some to know that four of your most important gauges, oil & fuel level, oil temp. & pressure are all dependent on variable resistors as sensors for the important data to be displayed! Consequently, when one of those gauges is malfunctioning, the gauge and wiring to the sender can be verified as working, but not necessarily 'calibrated' correctly, by substituting a simple, human-controlled variable resistor for the sensor/sender at the point where the vehicle wiring harness is terminated. Without even knowing what the range of the sensor resistance values are, I can say that on 99.9% of the vehicles on the road can be tested in the same way with variable resistors (potentiometers or rheostats) of 1000, 5000, or 10,000 Ohm (1K, 5K, or 10K) values with clip leads attached, one to ground, the other to the lead normally attached to the sensor. Radio Shack is not my favorite source for electronic parts, but they are everywhere, so I usually mention that cheap 'pots' (lingo for potentiometers) can be found there, even if the store 'associate' is somewhat limited in knowledge, they can usually point out where the components are in the stores.

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Warren Hall
1973 911S Targa