Temp gauge reads wrong?!?

[DK832]

Ran out of things to try: I've swapped a water temp gauge for an Autometer electrical one, sensor sits in the intake as usual. Ran wires to +12V ignition lead in the plug to the dash/gauges, ground to point behind dash, dash lighting and used the old original wire out to the sensor in the intake. When I use an IR temp gun the intake/sensor is 63°F but the gauge shows 150°F! When running at normal temp the gauge shows 250°F... I have tried 2 new Autometer sensors and 1 old used one (not Autometer), all have this misreading. I could find and add a resistor of (say 0.5 ohms) to the sensor wire to correct but WTF is going wrong here? Bad gauge or have I missed something entirely?

 

[D.Hearne]

Why'd you use the old wiring ? That could well be the problem.

 

[DK832]

Thanks for the input. Yeah, one of the first things I checked. Reused so I wouldn't have to open up the wire harness in the engine bay. It's fairly nice as it is. I measured the old wiring and it has the same resistance as a similar piece of new wire. The sensor has lower resistance as it gets hotter, so if anything the old wire should have the gauge showing too little.

 

[10secgoal]

Did you have the problem before the new gauge ? Because the autometer and other after market gauges use a GM ohm sensor. That and auto meter sensors go out all the time, if you have one of those in there. Did you use teflon tape, or over tighten ?

 

[DK832]

No problems b4, Autometer in there now, even tried a new Autometer too. And yes, I used teflon tape...?

 

[10secgoal]

Eh, can sometime have them read funny if the teflon blocks the ground. We use teflon paste for it. Did you have a sensor that came with it, or the stocker ? Think 99% of their stuff is GM ohm sensors

 

[DK832]

Ok, will try paste. The sensor came with it but I also tried a N.I.B. I had on the shelf. Also tried the original one that was on the old gauge (not Autometer). All show approx the same fault. I might try to borrow a second gauge to see if its just faulty...

 

[10secgoal]

They can get all fubar also if they are overtightened.