I just bought an '89 IROC Z with a malfunctioning temperature gauge. If the car is cold and I start it and run it will work until it gets to just below 200 deg. Then the needle slowly drops to almost straight down and will not move. It will stay there as I drive the car. When I get back in it after work the gauge will go to just below 200 deg and again slowly drop back down to almost straight down and not move again. It has repeated this process since I have owned it.

Any suggestions?

 

Try changing the gauge sending unit. Drivers side, front, between the exhaust ports.

 

I changed sending unit and it worked. Thank you

 

Ok, finally got to drive the car to work. Gauge went to 220 and dropped to just below 100 and slowly creeped back up to about 100. It would drop a little as I got up to speed on the hwy then back to around 100 in stop and go traffic. Temp out side was about 72 deg. I thought it would be around 200 deg during drive to work but it never did once the thermostat opened up.

 

I'd almost be suspicious of the t-stat being bad. It may open late and then stick open until the engine cools back down while parked. The gauge actually read in 20* increments, 100 really = 180

Does the gauge sweep to full hot when cranking the engine to start ?

Does it happen if it just sits idling (don't drive, just let sit and run) ?

 

Sorry to get back to you so late. I took the Thermostat out and put it in boiling water with a cooking thermometer. It opened and closed at correct temperatures.

The gauge does sweep to full hot when I turn the key on.

And the gauge will go to about 220 at idle before opening up then will go just below 100 and stay there and fluctuate very small amounts but will not get above 100.

Odd huh!!

 

I have an 89 IROC and in 1993 the gauge went bad and it drove me batty untill I finally changed it. I then bought a pillar pod and installed a bowtie water temp gauge, oil pressure gauge and trans temp gauge for a back-up. They also have radiator caps now with a built in gauge. I just got mine in two weeks ago and it works great. I just thought about that I have three water temp gauges on the car.

 

What do you mean read in 20* increments?