55.2-59 56 Chevy temp gauge

[jeffs56]

Hey guys I’m having a issue with my temperature gauge pegging out at HOT. I have the stock rebuilt gauge cluster and it just reads it HOT. I have a brand new temperature sending unit in it and still the same. I was told to take the Teflon tape off of the threads and try that. Any suggestions? Thank you

[mr48chev]

You don't want Teflon tape on it as that insulates it from the block and prevents it from getting a proper ground.

You did get a sender that is specific for a 1956 Chevy Truck?

[jeffs56]

Thank you I will remove it and try it. So you think that would cause the pegging HOT on the gauge?

[1project2many]

mr48 really hit on a good point. The original gauge calibration puts the temp gauge near the center of the range around 170 to 180 degrees. Running a 190 thermostat usually causes the needle to rest much closer to "hot." If your engine is averaging 195-205 that's going to put the needle at "Hot." I believe I installed a resistor installed inline to scale the entire temperature display. I can double check my parts list if you are interested.

[jeffs56]

Yes for sure. I appreciate it. I need to get this figured out lol.

[jeffs56]

Hey guys so I was trying to figure out the temperature gauge today. I was running the truck without the radiator cap on for about 10 minutes or so. The temperature gauge never moved from all the way far left (cold) until I reved the motor a few times then it jumped all the way to HOT. I unhooked the wire that is connected to the temperature sending unit in the intake manifold and the needle stayed in the HOT position. Any advice? Thank yoh

[1project2many]

What are you using for a sending unit? Where is it located on the engine?

[jeffs56]

We bought the 56 Chevy truck sending unit from classic industries, it’s screwed into the intake manifold

[jeffs56]

Also after driving the truck down the road the gauge was still pegged HOT When I parked it. Next day I went to try to figure it out and the gauge was still in the HOT position. I unhooked the battery cable and removed the 3 screws that hold the cluster in the dash. Once I removed the cluster from the dash the needle instantly dropped back down to COLD

[1project2many]

I never got back to this thread so I apologize.

I used the stock temperature sender with a resistor for my truck. It changes the scale slightly but it puts the gauge at about 3/4 when "normal." I do not have the resistance marked down so I'd have to figure it out.

It sounds like you may have a short or an issue with the gauge. The temperature sender changes resistance as it warms up. When it's cold it has 500 Ohms resistance. When hot it has 50 ohms. When the wire is disconnected the needle should be below C. When shorted the needle will go above H.

If you have an ohmmeter you can check the sender. Measure resistance with the engine cold and the gauge disconnected. Should be 500 ohms or greater. Start the engine and idle until warm. Resistance should go down to around 50 ohms or less.

If you have some resistors you could connect them between the gauge wire and ground to see how the gauge responds. Again, 500 ohms for cold and 50 for hot.

Also try moving the wire harness with the key on to see if the gauge goes to H. It might help to have a helper watching for the needle to jump around.

Edit: Is the instrument cluster powered when the key is off? Disconnecting the battery cable with key off shouldn't have affected anything.

[jeffs56]

I will try that. I was thinking maybe the hot wire from the gauge is tied into the alternator power and it’s giving too much juice to the gauge. Because the only time the gauge will go to instantly HOT is when I rev the motor or drive the truck

[1project2many]

I've also seen that type of result when there's a wire that is chafed or pinched. In that case if you ignore the wire long enough it usually gets worse.

Alternator voltage to about 14.5V should be ok. But if the wire is connected to the alternator that means it's also connected to battery. You should change it to ignition power.

[jeffs56]

I’m going to try to track that wire down and do some other tests. Very frustrating. Seriously thinking of just going with autometer aftermarket gauges. I mean even if I get these gauges fixed are they accurate enough?

[jeffs56]

I tracked the red wire down and it goes into the back of the fuse block in the gauge fuse, so that should be good

[1project2many]

Originally Posted by jeffs56

I’m going to try to track that wire down and do some other tests. Very frustrating. Seriously thinking of just going with autometer aftermarket gauges.

That could be expensive but at least you'd have peace of mind knowing the wiring and gauges work together.

I mean even if I get these gauges fixed are they accurate enough?

The gauges just give an indication of engine condition. They are nowhere near close enough for science. But I've used mine successfully since '94 or so...

[jeffs56]

Wow that’s pretty good. I know a lot of people still recommend the stock gauges. I don’t think you can beat the looks of them

[_Ogre]

Once you get the gauge working correctly, you'll get used to it
Not much accuracy between H-C, but I know when TRUK is within range
Personally I think stock gauges define the interior of TF trucks

[jeffs56]

Yea you can’t beat the looks of them for sure.

[1project2many]

Wow that’s pretty good. I know a lot of people still recommend the stock gauges.

I've learned over the years that some people get frustrated with wiring or electrical issues and quickly decide the only solution they will accept is replacing "everything." I feel in those cases it's better to accept that people want the peace of mind that comes from buying "all new." In some cases, people even set a minimum price on peace of mind. A used Dakota Digital gauge set selling for $50 that just needs cleaning up might be suspected of having problems and ignored but a new one selling for $500 is a smokin' deal. If you want to continue troubleshooting there's plenty of sharp folks on the forum who can help.

Personally I think stock gauges define the interior of TF trucks

I don’t think you can beat the looks of them

My first vehicle for the road was a '55 short box I built out of a pile of rusted and wrecked trucks. I had lots of spare parts around. Long before I knew how to tune a carb or calculate a gear ratio, I'd figured out how to wire up the dash lights in the stock cluster. I used to have one cluster hanging from the ceiling of my workshop in the barn, wired to a 12V transformer I raided from an old toy. The cluster would stay lit after the lights were turned off. I thought it was the coolest thing to walk into the dark room and see that cluster lit up.