johntorg

I have an 89 turbo S with an erratic Temperature Gauge. Sometimes it goes to almost full hot after 4 or 5 minues of driving. The voltage gauge also goes low when this happens. This led me to think it was the typical ground issue. I cleaned the grounds by the Cruise control computer and the one on the bellhousing, with no success. The car is definitely not overheating. If I turn the engine off while driving and then turn the key back on with the car coasting in neutral the gauge goes to its normal condition (mark 1/4 of the way up). When I restart the engine it usually goes back to showing hot, but someimes maintains the normal position for a while.

Are there more grounds that I should check?

I have another turbo S track car that I could swap the cluster with but would like to avoid this until I have exhausted all other possibiliies.

quinnfiske

The temperature sensor for the guage may be at fault. I replaced mine and the reading steadied out. It in the same general area as the DME temp sensor. That is, at the front of the cylinder head on the intake side. It has a single wire lead attatched to it.

badass951

I am almost positive both temp sensors utilize two wires.

Spidey944

You need a ground and signal wire. This is correct.

quinnfiske

Two wires it is, I just looked at mine. They are both .25 inch spade type terminals.

bearone

for me it was a bad alternator and replacing it stopped the fluctuations.

what voltage are you getting across the batt terminals when running?

87951

adrial

I'd check the wires going to the sensor and then replace the sensor itself if you're sure there's no air in the cooling system.

Zero10

There are 2 wires for the temperature gauge, however one is for the reading the other is for the warning light, it does not have a dedicated ground.

You mentioned that you cleaned the grounds in the engine bay, however you didn't mention the instrument cluster grounds. I believe if they were poor/dirty they could cause the same issue. If the temperature gauge likes to read hot, the first thing is to make sure that the engine isn't actually that hot. It's probably worth borrowing an IR thermometer or something similar to verify the actual engine temperature, just to be safe.

gstreev

You may want to clean the contacts on the sending unit and the connectors or put on new connectors.

johntorg

I cleaned the grounds near the cruise control computer and one set on the bellhousing (found this in another post). Are there others that I should check?

johntorg

I just checked the water temperature with my IR thermometer it read 176 on the radiator hose and coolant reservoir and 180 on the coolant gooseneck. So its not actually running hot. I will check the sensor later today. I forgot to mention it, but the oil pressure gauge is pegged high, even with the key off, so I may be pulling the cluster anyway. Any Ideas how to unstick the oil pressure gauge?

gstreev

I had these problems after I cleaned the engine compartment.
Did both occur at once?

johntorg

I just bought the car, so I don't know when it happened.

gstreev

You can usually tell if a sending unit is bad by checking the resistance, I just don't know what the
proper values are.

johntorg

I may have found the problem and it was ground related. I found a post about a similar problem and it turned out to be the negative battery cable end, where it attaches to the battery. As a temporary fix I shot some Doxit contact cleaner into the end of the cable and re-crimped it with a pair of vise-grips. So far no more problem.