C1 Temperture Gauge

[William P.]

I have a 62' that I have been chasing down the reason why my temperature reads max when engine rpm is high enough to drive the amps into the positive range. It doesn't matter how high the amps are, just above zero. What I have checked:
1)Sender is sending correct ohms at corresponding temperatures. I.E. at 170 degrees (measured with IR gauge) 138 ohms
2)Ohm values are the same at the sender and at blue wire at the gauge.
3)Pink wire at the gauge is 12v, matches the battery.
4)Gauge cluster is grounded correctly, ohm meter reads almost zero between cluster and negative on battery.

With all this checked is it possible that gauge is faulty? any help is appreciated. If the gauge is faulty, does anyone have a suggestion of how to repair it or who to send it to for repair?

Thanks in Advance
Bill Pearson

[Jack H.]

Re: C1 Temperture Gauge

Per the temp sender's temp vs. resistance spec, 170F should correspond to roughly 112-132 ohms to be in spec... Your reading of 138 ohms isn't that far off especially considering the temp error that could have been induced by IR reading of the actual coolant temperature via the rad hose. Bottom line, it sounds like you should TRUST your temp sender!

The only way your temp gauge should PEG to the high side is if it's seeing enough branch circuit current to emulate a 40-ohm to ground situation (skinned insulation in the harness wire from the temp gauge to the sender?), if your voltage regulator might be going a bit bezerk and driving the battery WAY above normal charging levels (13-14 VDC range), or you've actually got an internal fault in the temp gauge itself.

I'm curious as to how you measured 12 VDC though.... With the engine running and RPM up high enough (1500 RPM or so) to stimulate the V-Reg/Gen to actually supply charging current (as the car would experience under normal driving conditions), you should be seeing a battery voltage in the 13-14 VDC range.

Your next step might be to disconnect the wire at the temp gauge that runs to the temp sender and splice in a 'test' circuit. This should consist of a 1/2-W potentiameter running to ground whose resistance you can vary between, say, 300 and 40 ohms. Do NOT go below 40 ohms or you risk PEGGING the temp gauge off-scale to the hot side and perhaps damaging the gauge itself!

If you get clean, stable temp gauge response with the 'placebo' temp sender test jig attached, the fault is likely to be found in your wiring harness.... If you still get erratic pointer needle fluxuations, it's pointing to the temp sender itself and faulty internal inductance windings.

There are a number of shops who restore/rebuild gauges (search the archieves) and Corvette Specialties is just one with a good reputation.