Coolant Temperature Gauge Problems

[rwb137]

Ok This question is about my 1990 GST. Recently I notice my temperature gauge goes all the way to H and then two seconds later is sweeps very quickly back to the middle of the gauge. I thought perhaps it might of been a faulty thermostat. I replaced with the same result. Coolant level is a proper level and all air bubbles are removed. I then thought that the sensor itself for the gauge is faulty. I purchased a Beck/arnely gauge from Advanced and with the car still cold and not even running the gauge immediately read almost middle. So then I know that the aftermarket sending unit are not as good as stock. So I went to satan and 44 bucks later installed new oem sender. I put key in ignition and again immediately the gauge sweeps to the middle if you wait 20 seconds or so the gauge falls to the cold position. Take the key out wait a minute turn key back on same things sweeps to middle of gauge then 20 seconds later falls to cold. I also change the connector at the sender with a new thinking possible excesssive resistance.

My question is the sender input for the gauge go thru the ecu? I thinking that possibly the ecu is get screwed up. I change the capacitors on the ecu around every 5 years. I've owned this car since 1994. Car sit in garage a lot. this car has mild mods nothing serious.

 

[92AWDHX40]

If im correct the ecu talks to the coolant temp sensor, and the actual gauge is read from the spade sender, on the thermostat housing, you may have a bad gauge on the cluster.

 

[wrencher]

The coolant sender is the one with the yellow /green wire.

The ground has to be good @ the sender body to battery negative.
There is also a ground direct for the coolant gauge specific out of the instrument cluster.

I would bet your problem lies in the wiring somewhere.
Look/ print this;

 

[rwb137]

Thanks you for you replies. I replaced the Coolant temp gauge in the instrument cluster. I haven't had anymore issues with gauge since. I was surprised that you could still order this part from the dealer.