Anyone here ever fix a temperature gauge?

[MaximRecoil]

The temperature gauge in my 1969 Charger does nothing, even when removing the plug from the sending unit and grounding it with the ignition switch on. The oil pressure gauge and fuel gauge work fine (the ammeter is bypassed, but it worked before it was bypassed). I've already had the cluster out to do a solid-state 5V regulator conversion to it (which I did a couple of years ago), and I soldered those crimped-on power pins in place at that time. The temperature gauge has always been dead though; it was dead before I did that and it was still dead afterwards.

So if I remove the gauge from the cluster, is there anything I could try that might fix it?

[A383Wing]

it can be rewound with new wire..that's usually what burns up inside. Gibber here does them. Or you can buy a new-reproduction one

Before you condemn the gauge, do an OHM test across the terminals when dash is out...should be 21ohms I think

[MaximRecoil]

Okay, a Google search tells me these gauges use a bimetalic strip wrapped with nichrome wire. Nichrome wire is easy enough to find online, but it comes in various gauges. Do you know what gauge wire these gauges use, and about how much length?

[A383Wing]

yup..it ain't cheap either..ya gotta buy a roll, like I said before, contact Gibber here, he can tell you all about it

Bryan

[MaximRecoil]

My meter showed no continuity between the terminals, and when I got it apart, I could see that the original nichrome wire was broken, and it had nearly all of its insulation burned off (what little remained was black/charred).

Gibber sold me enough of the nichrome wire to rewire one gauge. It is a very tedious and fiddly job; the gauge is small and the wire is about as thick as a hair. I tested it when I finished by briefly applying 12 volts across it, and the needle quickly rotated all the way to the right, so it definitely works now. After getting everything back together and the instrument cluster reinstalled in my car, the temperature gauge still didn't work, so tomorrow I'm going to try a new temperature sending unit. The one already in the car is in unknown condition, because my temperature gauge has never worked since I've had the car.

[Pete in NH]

Wow!, Good going on re-winding the temperature gauge. I can't imagine what a tedious job that must have been.

Before you pull the temperature sending unit you might want to put an ohm meter across it. I should be somewhere around 60 to 75 ohms cold. You can also check your gauge calibration with some test resistors. 73 ohms should equal cold, 24 ohms = mid range and 10 ohms = hot or fullscale. You might have an open circuit between the gauge and the sender.

[Dino]

If all else fails, find a used gauge.  I got one off ebay last year around $20.  It was a fuel gauge but the ohm reading is the same and you can transplant the temp gauge faceplate by drilling or cutting the old rivets.  I installed plain rivets and painted them black as you can't see them once installed.

[MaximRecoil]

Wow!, Good going on re-winding the temperature gauge. I can't imagine what a tedious job that must have been.

Before you pull the temperature sending unit you might want to put an ohm meter across it. I should be somewhere around 60 to 75 ohms cold. You can also check your gauge calibration with some test resistors. 73 ohms should equal cold, 24 ohms = mid range and 10 ohms = hot or fullscale. You might have an open circuit between the gauge and the sender.

There's no open circuit; today I had my mechanic friend briefly ground the connector that plugs onto the sending unit while I watched the temperature gauge, and the needle went up when he did it. I already knew the gauge was functional after I replaced the nichrome wire yesterday because I bench tested it, but I did the test in the car specifically to eliminate the possibility of an open between the sending unit and the gauge.

Thanks for the information about testing the sending unit, I was wondering how it could be tested. So I assume you just place the meter's red lead on the threaded stud terminal and the black lead to ground?

Edit: I measured the sending unit when it was warmed up and it is showing 20 ohms. So I've verified that the gauge itself works, I've verified that the circuit between the sending unit and the gauge is okay, and the resistance of the sending unit is in the right range for a warm engine ... so what's the problem? Shouldn't the gauge be doing something?

[A383Wing]

if the original wire was burnt up and fried, most likely it degraded the bi-metal strip it's wound around...the strip "flexes" as the wire around it warms it up. I think if you are having this much trouble with the gauge, you should just think about getting a new one...the one you have will never be accurate again

Bryan

[MaximRecoil]

if the original wire was burnt up and fried, most likely it degraded the bi-metal strip it's wound around...the strip "flexes" as the wire around it warms it up. I think if you are having this much trouble with the gauge, you should just think about getting a new one...the one you have will never be accurate again

Bryan

I think the gauge is just way out of adjustment. The needle will move when you overload it with 12 volts, but the normal 5 volts won't do it. The needle is all the way to the left (and always has been since I've had it), resting on the side of the face. When I get up the gumption to tear that dash all apart again, I'll adjust it so the needle rests right on the line or just before it.

Accuracy, in terms of the needle position lining up with the exact number which represents the actual temperature of the coolant, doesn't matter. As long as the needle moves to some position between cold and hot when the engine is warmed up, that will serve just fine as a reference point. My fuel gauge isn't accurate either (aftermarket sending unit combined with a gauge that is likely well out of adjustment and likely has no insulation left on the nichrome wire), but I know where the needle goes when it is full and when it is empty, which is all that really matters.

[MaximRecoil]

It is now working.

With the car off:



And this is where the temperature gauge needle leveled off after idling on a hot day for 15 minutes (the needle didn't go any higher after about 10 minutes:



The bimetallic strip was bent/warped out of shape, leaving the needle resting against the side of the face plate, all the way to the left, and without the faceplate to rest against, it went even further to the left. So I removed the needle (another fiddly job) and straightened the bimetallic strip. Then after reinstalling the needle, I adjusted those toothed levers until the needle rested just before the cold line on the face. That did the trick.

The other two gauges' bimetallic strips were both in good shape, nice and straight, and their nichrome wires were okay, though the insulation on both of them was quite browned (but not blackened/charred). Both of them tested at only 12.5 ohms (instead of 20 like they are supposed to), so they probably are not accurate, but they do work. I adjusted the needles on both of those too so that they rested on the line. I can see already that it makes them both more true (for example, my gas gauge showed empty before, even though there's still a good deal of gas in there).

All my gauges work now, well, except for the clock, which I don't care about, and I have the alternator gauge bypassed, but it worked before I did that.