1956 temperature gauge/sending unit

[woodeye]

My temp gauge is pegged at hot with ignition off or on, but the wire isn't connected right now because I've got a mechanical gauge hooked up.
When i ground the wire from the old sending unit it goes all the way to cold.
I got a new sending unit from my local parts place and when we bench tested it it went all the way to cold.
when we tried it in water that we gradually heated it only stayed at cold.
When we disconnected the ground wire from the sending unit the gauge went all the way to hot.
The gauge does move to hot with key on if the wire is un-grounded.
Does this gauge need a unique sending unit, because the one from CASCO was $85, and the one locally was only $33.
The parts house said this is supposed to work with an OE gauge, which is what I think I have.
Thanks Jeff

 

[minicheckmate]

How the wire? It almost sound like the wire might be all corroded and cracking so you're not getting the proper signal? Just a shot in the dark guess.

 

[doug7740]

My temp gauge is pegged at hot with ignition off or on, but the wire isn't connected right now because I've got a mechanical gauge hooked up.
When i ground the wire from the old sending unit it goes all the way to cold.
I got a new sending unit from my local parts place and when we bench tested it it went all the way to cold.
when we tried it in water that we gradually heated it only stayed at cold.
When we disconnected the ground wire from the sending unit the gauge went all the way to hot.
The gauge does move to hot with key on if the wire is un-grounded.
Does this gauge need a unique sending unit, because the one from CASCO was $85, and the one locally was only $33.
The parts house said this is supposed to work with an OE gauge, which is what I think I have.
Thanks Jeff

Here is a quick check of the temperature gauge:

• Disconnect the wire from the temperature sending unit
• Turn the ignition switch to the “Acc” position
• Touch the wire from the sending unit to ground, for not longer than ten seconds
• Check to see if the gauge moves from the rest position (Hot) to the left of the cold position

If it does, suspect the sending unit as the faulty component. If it doesn’t, then the problem exists in the gauge or wiring. If the problem turns out to be a defective gauge, replace both the gauge and sending unit. It’s a good idea to also inspect the wiring.

REST POSITION​

WIRE GROUNDED POSITION​

The X’s on the diagram below indicate the places where you can check the system.

doug7740
1955 Thunderbird Blue

 

[woodeye]

Hi thanks to both minicheckmate and Doug for your thoughts.
We ran new wires to eliminate that as a problem.
grounded the old wire and the gauge responded the way doug described.
When I tried a new sender, that was supposed.to be correct for a 1956 with a 312 cid motor, dipped it into water, which we heated, the gauge didn't respond.
I'm wondering if if anyone is aware of a special sender that should be used with an OE gauge.
CASCO offers a replacement gauge and sender, or just a sender that is to be used with a replacement gauge.
This suggests to me that the OE sender might be unique need it's own sender.
Just hoping someone is aware of the issue and what the solution might be.
Thanks Jeff

 

[doug7740]

When you tested the sending unit by dipping it in the heated water, how did you wire the sending unit to the gauge? Was the sending unit grounded? CASCO sells a temperature sending unit that is to be used with the original gauge unit, or a replacement gauge and sending unit as a set. If your gauge is original are you really going to trust a gauge that is 68 yeaars old! As I said above, replace both the gauge and sending unit as a set. CASCO calibrates the gauge to the replacement sending unit.

doug7740
1955 Thunderbird Blue

 

[Pink T-Bird]

@woodeye - For your heated water test you still need a ground in the circuit. The sender provides a variable resistance, but without the sender grounded you have an open circuit, same as if the wire at the sender is disconnected. Connect a jumper to the body of the sender and to the engine block, or other ground point. Then retry your hot water test. You also need the water to be hot enough to be able to move the gauge a little, like 130 - 150 F, which is hot enough to burn you, so be careful.

 

[milspecagent]

We are having similar problems with our temp gauge on a new rebuilt 1956 original engine that just went back into my 1956 T-Bird. I don't exactly know what the problems are, but I will advise my mechanic of all of this information and then get back to you. Thanks. I believe this may prove helpful for our situation as well. I do know that we are attempting to use a new sending unit with the old temp gauge and have similar indications. HLB3

 

[woodeye]

I ultimately purchased a new gauge/sending unit package and it seems to be working. it was a bugger to get out and in ,but we got it.