I have been having a problem with my temp gauge lately. I would be driving the first time after the car sat a few weeks and the gauge would peg after about 10 miles. First time it happened, I shut it down then restarted it and it went normal. Second time I moved the cap 1 notch and back (I know, I know) and it was OK. Radiator is full with car cold and level. I figured thermostat was sticking so I ordered one from GM. (Setup: L98 TPI complete engine including water pump from a '90, Griffin aluminum radiator, dual C4 electric fans-1 ECM controlled, 1 sender in head on at 220, good sealing, has a spoiler) Car has never gone over 200 even sitting in summer traffic with a/c on. Anyway, it had 5 years on the old coolant so I figured it was time for a change anyway. I rolled it up on ramps, removed the lower radiator hose and drained it, removed the cap, removed the upper hose from the t-stat housing, removed the t-shousing and t-stat. Ran water through the radiator until it was clear. Ran water from intake (where t-stat was) out the lower hose until it ran clear. Re-installed lower hose. Filled the radiator slowly until the intake (t-stat hole) was full of water. Reinstalled t-stat, housing, upper radiator hose. Filled it the rest of the way. Started the car, backed it off the ramps. I should have immediately looked at the gauge-didn't, but after 3 minutes I looked and it was pegged. Shut the car off and got my scanner. Scanner says temp is about 120 at this point. I let it warm up and all seemed normal as far as the radiator being warm, hoses hot but not hard, running normal, etc. Gauge still pegged. 1 fan came on at about 200 and off again at 195 (according to the scanner) just like it should.

I removed the wire from the temp sensor-no change
I grounded the wire from the temp sensor-no change

I assume I have a wiring problem or a gauge problem.

1) Does anyone have a chart on temp sensor resistance vs: temperature? I have a bunch of manuals, but can't find this chart. I know I have seen one somewhere. I know this is not all the problem, but maybe it's what stuck the gauge in the first place?
2) Anybody have a gauge peg and just get stuck?

I guess I will pull the cluster, but I don't want to. Anything I might be overlooking?

 

yup wiring problem. I recall it pegs with an open circuit.

 

Thanks, I'll look at that before I pull the cluster,

 

Check gauge and wiring by leaving open (pegged, full scale) and grounded (0 temp reading). If those check out, it's your sending unit. If not, it's wiring.

 

I did that already and it did not change. Gauges were rebuilt when I did the car. I am hoping it is wiring, but can't explain why it has acted how it has acted.

 

hold ona sec, I thought that with the circuit grounded...ie remove the sender wire and touch it to the frame, it should peg the temp guage out completely and then remove it from the frame it should go back to zero??? am I wrong or just not understand the open and closed circuit terminology??? YES... i still dont have mine working in my 72....lol


thanks,

Sully

 

To be honest, Sully, I didn't remember which way was which either. I just remembered that "open" circuit went full-scale one way and "shorted" circuit went full-scale the other way. If the gauge moves at all, it's not the gauge; if it swings both ways [when doing the above test], it's not the wiring; else, it's the sending unit. So, which direction it moves with short/closed circuit doesn't really matter.

 

Update:

It was the gauge. The wire checked good so I pulled the cluster. I had a spare gauge that went to zero when I plugged it in. I was going to live with the used look, but after putting it in it does not move off zero when the engine warms up. I am going to send off the one from the car to get rebuilt so that they all match up. Luckily I did not fully reinstall the dash yet.