[66tri-hb]

I have just completed my 66 gto rebuild and my temp guage starts at 180 it never goes to zero but does seem to be working. do I have something hooked up wrong? This is the way it was when I started but I thought when switch was turned on it should go to zero. Help needed!!

[Greg Reid]

I'm not 100% positive on this but here are my thoughts on possible reasons it won't go to zero....

1. Many electrically controlled sending units...as opposed to mechanical units....read zero when shorted to ground and full sweep when open. The electrical sending unit gives the gauge something between a dead short and open dependent ont he temperature, the pressure or whatever is supposed to be measuring.
With that in mind, a gauge that won't read zero would indicate a poor ground.
Not sure what kind of sending units you have so...If it's electric, you might make sure the sending unit is making a good electrical ground to the block. Sealant or something of that nature on the threads could interfere with it.

2. It's a temperature gauge...so, it's going to read the temperature. Unless the temperature is zero...it's not going to read zero.
Just some thoughts...

[merlotgoat]

You may have a wiring problem with that gauge. It's been a while since I've had a set in my hands, but I think they way that gauge works is that there are two circuits in the gauge--one pulls the needle one direction, the other pulls the needle the other direction. There is a resistor that looks like a small stick of gum that helps this tug of war work. The sending unit is the variable ground, the other is the fixed ground. When the engine temp is cool, the resistance from the sender is higher and the needle gets pulled to the left. When the engine gets hot, the sender decreases resistance, winning the tug of war and pulls the needle to the right. Did you have the gauge apart? New wiring harness? or did you fabricate your own connections for a conversion from non-rally to rally gauges? Is your dash properly grounded?

[66tri-hb]

Bob
I have just started working on the dash. for some reason someone did have some wires pulled down and there was foil on the old fuses. the car has been in a gerage 25 to 30 years and the dash and all guages are original. I do need to look at the temp guage more now that I have some info to go on . I sits in the middle 180 but does move up some when running. thanks I may need you again soon when I take a good look.
Hunter

[Greg Reid]

Sorry, didn't occur to me that you were talking original rally gauges. I thought you were speaking of aftermarket electric or mechanical gauges.