Temperature gauge all the way to the right

[joshkbomb]

Yesterday my temperature gauge decided to peg itself all the way to the right. It doesn't budge even when I unplug the temperature sensor. I figure this is either a ground problem or the gauge is bad.

Is there any way to know whether it's the gauge or the wiring (without having another gauge to test with)?

 

[dremu]

More than likely wiring, either the green wire from the sender to the cluster, or on the cluster itself. (The flexible circuit "board" on the back of the cluster can get corroded or heat-damaged over the years.)

I can never remember if the gauges ping like that when they're open (i.e. disconnected) or shorted (i.e. the wire is grounded.) If you have an ohm-meter, though, it's easy to test. Undo the tang from the send, and check resistance from that tang to a ground (body, battery negative, whatever.)

If there's 0 ohms or dang close, then the green wire is shorted to ground (insulation chafed off or melted somewhere.) Trace it and tape it up, making sure it can't get caught in the steering column or exhaust or whatever caused the problem

If there's a stupidly high resistance (over several thousand ohms, or whatever your meter says when the leads aren't touching, i.e. infinite resistance) then the wire is open, i.e. cracked or disconnected somewhere. Trace it, maybe look for a place where the wire is bent weird 'cuz the metal inside is busted but the insulation is still there.

If there's some resistance ("some" being, I donno, over 50 and less than a coupla hundred ohms) the gauge is okay and something else bad happened.

-- A

 

[joshkbomb]

So the resistance from the sender wire to ground was 0 ohms. I inspected the green wire and couldn't find any place where the insulation was anything other than perfect.

I then pulled the gauge and it is 0 ohms between the two side connectors. Does this mean the gauge is bad?

 

[dremu]

I thought the gauges had three wires ... maybe four. I never understood the damn things, two electromagnet coils or something.

You might go to the local pick-n-pull and test one there, worst case just buy it... but the gauges don't tend to fail much

-- A

 

[joshkbomb]

The gauge does have three wires, two are silver (the ones I tested) and one is copper colored. I guess I have to go to the yard to get a few other things as well anyway. It would have been nice to be able to figure this out, but even my factory service manual doesn't explain how the gauge works. Oh, well.

Thanks for the help anyway!

 

[dyeager535]

Check the small ceramic plate on the back of the gauge. I've seen those go bad, another one (from just about any GM gauge) will work, but I am under the impression that those are a specific resistance (you'll notice they are color-coded and not all the same), to "tune" the gauge.

I wouldn't toss the gauge until I'd either swapped that piece or at least tested it compared to another.

Should be three wires. +,-, and the sending unit wire. No wires should go to the gauge, your post confuses me. Printed circuit board should be delivering all three of those to the gauge, nothing else. Or did you disassemble it?

 

[British Slave]

Check the nuts on the gage terminals on the back of the gage. If they are tight, replace the gage, if loose tighten and check gage again.

 

[joshkbomb]

Sorry, I meant three posts on the gauge.

I'll definitely try swapping the ceramic plate. I imagine the gauges I find won't be as nice as mine, so maybe I could swap parts and fix it.

Hopefully I can get to the junkyard next weekend and see what they have. Whatever I find out, I'll update this thread.

 

[dyeager535]

I don't believe it matters which gauge(s) you get the ceramic piece from, but you'll want to play around with a few of them to confirm that the resistance is or is not the same.

Since you see different colors on other gauges in the same cluster, my gut tells me it's how they made sure the gauges were as close as possible from the factory.

 

[joshkbomb]

Well, I ended up finding a nice temp gauge from a Chevy truck yard for $15. It works so I just bought it, plugged it in and that's that. I don't want to try installing the new ceramic piece on the old gauge (to see if that's what was wrong) in case it shorts or something weird.

While I was there, I also scored a small fuel gauge. I've been wanting one of these for a few years now to replace the mis-shapen Corvette gauge I installed when I did the tachometer. It didn't read right, but I'm messing with different ceramic pieces and it looks like the ceramic piece from the Corvette gauge is the right one. I'll find out how well it works when I fill up in a few days.