Chip Gregg

I have been having issues with the gauges on my '86 951 that make it hard to tell if I'm actually having engine issues or not. The car runs flawlessly, but since I've had it the volt meter is usually at 10v and will occasionally rise to 12. The temp gauge will creep up to the red sometimes at red lights, but if I shut the engine off and just click the key to "on" the gauge will read in the middle(normal). The oil pressure gauge usually reads 4-5 regardless of temp or RPM and will occasionally bounce severely. Today the oil pressure gauge started dropping into the red and lighting the warning light at idle, but if I turn electrical things off the needles will move. If I'm actually have oil pressure issues are there any indicators such as loud lifters to look for?

V2Rocket

Guessing a ground problem in the cluster, or the wires are loose on the sender.
At least in early 944, the gauge light and the oil pressure gauge are totally separate from eachother. So maybe there is a real issue?

Van

Same on late cars - if you're getting both, I'd be very suspicious/cautious.

mytrplseven

The connections on the oil pressure gauge seem to be a frequent problem due to looseness. Because it's not too hard to check them, I'd start there and then on to the matter of cleaning all the grounds.

Chip Gregg

I'm going to clean grounds and check the sender. I hate the gauges are so wakadoo because I just don't know. I suspected the sender because of the bounce and the fact it has been reading above 4 even hot at idle. That red light is scary though. When I turn off accessories the pressure gauge will jump up and the light will go out.

Chip Gregg

One other thing, will lifters get noisy or any other such indicator be noticeable with low pressure?

Voith

Eventually rod bearings will become noisy and you don't want that. Make sure your pressure is ok asap.

mytrplseven

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mytrplseven

My gauge was indicating full scale and it wasn't the reversed connections. A VDO replacement sensor solved the issue, including the low oil pressure warning light.

Chip Gregg

I cleaned the easy to get to grounds and the pressure gauge and volt meter are reading higher. Oil pressure gauge will bounce like crazy and read erratically hi or low. I did notice as I turned on lights and the ac blower the gauge would drop lower and lower. Going to get the other grounds and order a new pressure sender this weekend. Thanks guys!

944Ross

I'd start by throwing a quality voltmeter across the battery and compare the reading to the dash gauge. Flip on accessories and see how it responds.

My OP gauge was doing some wonky things, it was the sender. Leaking oil all over too.

dr951

In many of these cases, it is bad wiring / poor connections. The wires are 35 years old and the OP wire harness runs across some of the hottest parts of the engine, esp in a 951. The wire insulation gets baked, become like crispy bacon, breaks off the wire then you get problems.Then at the OP Sender / switch there can be oil on the terminals from past oil filter changes that drip oil everywhere. If the terminals are dirty and oil soaked, they could be partially open (higher and variable resistance). Also, if the body of the sender is oily near the terminals, an unintentional ground path can be established since the metal body of the sender is at Engine Ground potential. If the wire harness insulation is broken in several places, the wires could be shorting to ground. Also, the insulation of wires give the wire strength against vibration work-hardening. With broken or cracked insulation, wiring can vibrate, and like a tab top on a beer can, eventually break off. Sure the original VDO brand Oil Pressure Sender / switch (OPS) can go bad, but they are amazingly reliable units. On my '86 951 with 130k miles, the original OPS that I replaced (!!) was in fact working fine! Doh! It was the wiring harness in my case - the terminals were gummed up and filthy and several strands of wire were broken. And later I found the two-wire harness was partially broken under the intake manifold - a major hassle to fix. The wire insulation crumbled in my hands as I handled the wires! The turbo engines get REALLY HOT and the harness is only inches from the red-hot turbo. Anyone for baked harness with a side of gauge malfunction?

Tiger03447

After you change out the sender, keep the old one. Cut open the sender and discard the guts, keeping the threaded portion. There are plenty of direct reading gauges with a nylon line at your local FLAPS. Drill/bore and tap the old portion of the sender to the nylon line fittings. Now you have a pressure gauge that is direct reading for pressure checks. Since the new gauge (cheap) is in lbs/sq inch, you'll have to do a conversion to bar for comparison (14.7lbs=1 bar approx.) to the VDO gauge in the dash. (note: you'll have to bleed the air out of the nylon line before you can get a good reading) There are also copper lines available for this..I am thinking of a SunPro gauge and their accessories. Just a thought to help keep your mind at peace..Just sayin..

vetter59

I had a very similar problem with my '88 NA, turned out it was a poor crimp on spade connector at oil pressure sender -wire was actually loose inside crimp connector, it had been replaced before -Installed new crimp spade connector - fixed the problem.