88 Fiero GT temp. gage (Page 1/1)
Duck 1 JUN 25, 10:54 AM
My dash temp gage will not respond. I have changed temp sending unit on engine but still not working. When I first start the car , the gage swings about 3/4 and then goes back to full right position. The fan sending unit works as it should to come on when temp gets hot enough. Anyone have any suggestions ?
Vintage-Nut JUN 25, 12:00 PM
The '88 GT coolant temperature sensor has a two-wire electrical connector:
One feeds the gauge and the other feeds the high-temperature warning light/bulb.

However, the coolant temperature gauge is infamous for "pegging" when the engine is started.

Many re-wired the gauge, see the schematic below:
Duck 1 JUN 25, 07:07 PM
Thank you very much for that information.
Duck 1 JUN 25, 07:37 PM
If I switch the wires on the temperature sending switch and switch the wires on #11 and # 13 behind the instrument panel will the red light and temperature gage still work normally if engine starts to overheat?
Vintage-Nut JUN 25, 10:59 PM
IF your factory wiring is correct meaning you don't have problems in the circuits; YES

From https://www.fierofocus.com/...osails/tempgage.html

"The factory wiring applies a full 12 volts across the temperature gauge when the ignition key is turned to "Start". This momentary connection is called the ‘Bulb Test’ position and shows at a glance that critical warning lights are functional. Unfortunately, it appears GM made a mistake and connected the ‘Bulb Test’ feature to the Coolant Temperature Gauge instead of the Coolant Temperature Warning light.

The fix requires swapping two wires on the coolant sensor (GM 25036809) and two wires at the back of the instrument cluster. The result is the ‘Bulb Test’ will light the Coolant Temperature Warning and the Coolant Temperature Gauge will works without "pegging" the maximum range."

Step #1: Remove the plastic connector housing from the coolant sensor and swap the wire locations.
Step #2: Remove the instrument rear cover and swap locations C2 #11 with C3 #13

Enjoy!

[This message has been edited by Vintage-Nut (edited 06-25-2023).]

Duck 1 JUN 26, 07:39 AM
When i put the new temp sending unit in the engine I attached it to the 2 green wires . The next thing I did was to ground each connection temporally and watch the red light and then the temp gage to activate. I am assuming from that test the temp sending unit is installed correctly. My understanding in reading your instructions that the next thing is to switch wires 11 and 13 on the back of the instrument panel. Is that procedure correct ?
Rhodesia1977 JUL 23, 03:37 PM
Strangely enough when I first got my 86 GT, mine wasn't working either. I switched the wires at the temp gauge sender sensor on engine and it has been working since. It's fairly accurate. +/- 12 degrees.