1950s thermostat gauge question

[Daffer]

might be jumping to conclusions I just fear im not getting a reading on my temp gauge in my 1950 cadillac. I did the ground test and boom right away it jumped to the max while the car was just turned to ignition but not on. I also replaced it with a new one when the heads were off just because i wasn't sure if the original one worked so i felt might as well do it when its easy. now Ive started the car but haven't done a test drive yet since I had a small fuel leak which looks to be fixed but when I had it running for maybe max 15 min and I did rev it a few times nothing seemed to pop up on the gauge. Im wondering how long does it normally take to have a reading pop up on the guage? thank you!
-Joshua

[Davidcamper]

On my 51 I have to let it run about 20 minutes to start moving the gauge. It also depends upon the current ambient temperature outside. If you are in Texas heat in July, it should start moving sooner rather than later.

[Davidcamper]

Also, you say you replaced it? Is your car still 6 volt? If so, is new gauge 6 volt? Is sending unit on head 6 volt?

[Daffer]

On my 51 I have to let it run about 20 minutes to start moving the gauge. It also depends upon the current ambient temperature outside. If you are in Texas heat in July, it should start moving sooner rather than later.

I'm in Illinois but its been pretty hot in the 90s, hopefully something will show up

Also, you say you replaced it? Is your car still 6 volt? If so, is new gauge 6 volt? Is sending unit on head 6 volt?

yea everything is 6v, I even made sure when purchasing the new sending unit

[J. Gomez]

Joshua,

I would suggest to clip a jumper between the temp sender body (ground) and the terminal end (wire), this should validate the sender is properly grounded.

I do not know the resistance value of that era temp sender but this older post shows to be around 250 (cold) which will drop when coolant temp rises. You could test the sender resistance drop function by placing it in water while heating the water.

[Jay Friedman]

The sending unit grounds through the threads in the head, so make sure the threads are clean and there is no paint on them.

[Daffer]

The sending unit grounds through the threads in the head, so make sure the threads are clean and there is no paint on them.

Yea when I painted the head I kept the old unit in and taped it off then replaced it after some thinking but it ended up leaking a little and I had to unscrew it and add some teflon tape to the end in a way it just fills in the very end but not make it so it couldn't ground

[Daffer]

Joshua,

I would suggest to clip a jumper between the temp sender body (ground) and the terminal end (wire), this should validate the sender is properly grounded.

I do not know the resistance value of that era temp sender but this older post shows to be around 250 (cold) which will drop when coolant temp rises. You could test the sender resistance drop function by placing it in water while heating the water.

Ill give it a try. so just a wire from the brass body to the sender wire?

[J. Gomez]

Ill give it a try. so just a wire from the brass body to the sender wire?

Joshua,

Yes, just clip it from the sender brass body over to the sender terminal wire, an alligator clip wire should do it the gauge should go to the "H" side if the sender has a good ground from the block.

Good luck..!

[Daffer]

Joshua,

Yes, just clip it from the sender brass body over to the sender terminal wire, an alligator clip wire should do it the gauge should go to the "H" side if the sender has a good ground from the block.

Good luck..!

I think i did something similar i connected a wire to the body the connected it to a ground screw on the firewall and turned the key to ignition it immediately went to the very end the "H" side, so im assuming that means the dash guage is good but im also guessing I'll have to really warm the engine up to see if the sending unit is grounded in the head properly because its a brand new  unit (hopefully i can just warm it up by running it in the garage, because i kinda want everythingswuared away before a test drive)

[J. Gomez]

I think i did something similar i connected a wire to the body the connected it to a ground screw on the firewall and turned the key to ignition it immediately went to the very end the "H" side, so im assuming that means the dash guage is good but im also guessing I'll have to really warm the engine up to see if the sending unit is grounded in the head properly because its a brand new  unit (hopefully i can just warm it up by running it in the garage, because i kinda want everythingswuared away before a test drive)

Joshua,

Your test by using a body ground to the temp sender contact indeed validates the wire and gauge integrity of the wire and the functioning of the gauge.  My suggestion as well as to validate the wire and gauge would also validate the temp sender has a proper ground to the engine block.

Although the sender maybe new with clean threads the threads at the engine block may not be, no rust, paint, sealer, etc.. It is extremely hard to offer a suggestion/solution to a problem remotely without knowing all the variables for a solution.   

Good luck..!

[Daffer]

Joshua,

Your test by using a body ground to the temp sender contact indeed validates the wire and gauge integrity of the wire and the functioning of the gauge.  My suggestion as well as to validate the wire and gauge would also validate the temp sender has a proper ground to the engine block.

Although the sender maybe new with clean threads the threads at the engine block may not be, no rust, paint, sealer, etc.. It is extremely hard to offer a suggestion/solution to a problem remotely without knowing all the variables for a solution.   

Good luck..!

Ohhh ok Ill give your test a try, hopefully it has a good ground. That really a smart test wow. Thanks I'll update everyone