PorscheG96

My 968's temp gauge would frequently sit at the 10 o'clock mark and beyond when driving in the city or waiting at stop lights. It climbed normally from 7 o'clock to 8 or 9 o'clock positions until warmed up in the morning, but after that it often appeared to be overheating. I also saw that the gauge fluctuated between 10 o'clock, pegged at the top, and 9 o'clock when driving but usually tapping the plastic gauge cluster shroud w/ my finger would stop these rapid changes. The gauge was obviously being wacko but I wasn't sure if my car also had some kind of cooling problem since it spent so much time at the 10 o'clock position.

So the other day when changing the battery I decided to pull out the gauge cluster again. Looking carefully at the back there are two oval-shaped caps fastened w/ 10mm nuts [1 each]. Removing the nuts & washers allows both oval caps to be removed and they contain brass grounding posts as pictured:



I proceeded to clean all of the brass surfaces of grime and corrosion then put everything back together. If you do this then be very careful not to shock, bend, or overtighten anything on the back of the cluster. When I put it all back together I connected the new battery and road tested it for a couple of days. Now my temp gauge rides slightly below the 8 o'clock mark whenever the car is moving. When it's stopped, the gauge goes to SLIGHTLY ABOVE 9 o'clock [but nowhere near 10 o'clock] before the fan relay clicks and temp reading returns to 8 o'clock. This appears to be perfect operation so I'm stoked w/ the result.

I've seen lots of 944/968 owners post about the engine running hot and folks suggesting radiator temp switch or fan relay replacement, new thermostat, fan resistors, etc. Before you spend a lot of money diagnosing the problem, I'd suggest making sure that your temp gauge is grounding properly and cleaning it like I did - it's free. You can also bleed the cooling system which is what I tried first but that didn't help.

In the next few days I'll post whether this fixes the fuel gauge problem as well. I've read about folks filling their gas tanks but the fuel gauge reads between 3/4 and 4/4 full, and that's what mine does.

Luis de Prat

Great write up. I had heard about the sender units giving bad readings from soiled or corroded contacts, but never thought of the instrument cluster itself.

I was planning to pull mine to refresh the bulbs and will now have a look at these grounding posts. You took them apart to clean them it looks like?

Shamus

Thanks for the info - this project is on my winter project list...

Luis de Prat

Just took the instrument cluster out to replace the bulbs yesterday and did this while I was in there. I'll see how it goes and report back once I reset the airbag light.

The bulbs weren't out, but they were really dark. I also lined the reflectors with foil and the lighting is much improved.

RajDatta

I had a similar problem and it looks like I had corrosion on my circuit ends where the harness connectors plug in. I swapped out the cluster while moving all my old guages to the new cluster. Problem solved.
Thanks for the writeup Trevor.
Raj

PorscheG96

Luis, I'm curious why you have the rheostat pictured. Did you replace that too?

Raj, why did you swap out the gauge cluster? I did another neat project yesterday that I'll post up later!

Luis de Prat

I took that pic for someone in another thread who's putting together an "LED dimmer" of sorts. Since LEDs aren't adjustable via the regular rheostat.

Posted it here to show the blackened bulb. This was all on the 1990 S2, btw.

RajDatta

My problem was the circuit board. I had tried swapping guages and those pins but the problem existed. After swapping the cluster, the temp guage is 100% accurate now.
Raj

Thom

Thanks for the write up.
The temp on my 944 S2 has shown incorrect readings for some time so I will look into this.

On a similar note, is it possible to adjust the travel of the fuel gauge ?
With a full tank it does not reach the "full" position. I checked the probe in the tank by taking it upside down and it still won't top up.

PorscheG96

I'm hopeful that the fuel gauge problem will be fixed by cleaning the grounding posts as well, but I won't be filling up to test it until I head to the gas station later this week. I'll post an update either way.

Luis de Prat

Me too. I lightly sanded them all with 2000 grit paper. Kind of wishful thinking, though, given that practically all of these cars' fuel gauges read the same way.

Luis de Prat

A quick heads up before people start pulling their instrument clusters to do this.

After putting the cluster back in the dashboard and starting up the car I now have a completely dead temperature gauge, and the fuel gauge pegs at 4/4 even though there's less than half a tank in the car.

Now that I think of it, when I brought the instrument panel home from the garage to work on it, I could hear a rattle inside. After carefully separating the cluster, I found the following loose part that was causing the rattle:



It's too small to get a good photo but there's a bit of green glue on the head, so I suspect it broke loose when pulling the instrument panel.

I don't think Trevor's suggestion to clean the grounding posts has anything to do with these 2 gauges becoming inoperative, since I cleaned all 4 grounding posts in the same manner and the oil pressure and voltage gauges work correctly.

Rather I think removal of these delicate parts can cause "collateral damage," something I keep forgetting when working on these 15+ year-old cars! To think that all 4 gauges were working normally before, but I thought I'd try this to see if there was any improvement.

I'm going to pull the instrument panel again to check the temperature and fuel gauges, but if anyone can shed some light on what that tiny flathead screw is probably for, I would much appreciate it.

PorscheDude1

I maybe wrong, but I think that screw could be a "grounding lug" between the gauge in question and the ground trace on the flex circuit.
If you reinstall that screw in the correct place, it may fix your gauge problem.

RajDatta

From what you are saying, you are in "fail mode" for the two guages. As suggested, you are either not getting juice to them or have a grounding issue.
Raj

PorscheG96

Don't know what that screw is, but are you sure that all three gauge cluster harnesses are attached completely? It's really easy to have one that isn't fully connected because of the tight working space behind the cluster, especially if any of the 6 clips are broken on your harnesses.