Temperature Sending Unit

[john lokay]

I have a couple of questions concerning the temperature sending unit for a C2:
1) The sending unit in my '66 coupe reads 685 ohms when cold. I read earlier posts that the sending units for a C1 sould read about 700 ohms when cold. Is the 685 reading pretty close to where it should be?; 2) Were the type of sending units used for all C2's, big and small block, the same?; 3) Were the sending units used in the C2 the same as those used in other Chevy passenger cars at that time? Thanks

[Joe L.]

Re: Temperature Sending Unit

John-----

I expect that your 685 ohm reading is probably well within the acceptable range for the sending unit. I'm not positive of that, but I fully expect it.

The same sending unit was used for all 63-67 engines, small block, big block and, likely, even medium block if they had made any. This unit was of GM #1513321. It was a button terminal unit.

Many other GM cars of the period used this same sender. However, it was only used for cars with gauges, NOT overtemp warning lights.

[Joe L.]

Re: Temperature Sending Unit

John-----

I expect that your 685 ohm reading is probably well within the acceptable range for the sending unit. I'm not positive of that, but I fully expect it.

The same sending unit was used for all 63-67 engines, small block, big block and, likely, even medium block if they had made any. This unit was of GM #1513321. It was a button terminal unit.

Many other GM cars of the period used this same sender. However, it was only used for cars with gauges, NOT overtemp warning lights.

[Joe C.]

Re: Temperature Sending Unit

John:

The best way to verify accuracy of your sender/gauge system is to put the sender on a pot of water with a thermometer, hot wire it to your gauge, heat the water(very low flame to produce a slow rise) while monitoring the rise in temp. with the thermometer (known accurate) and compare to the gauge reading. This is tedious, and you may have to repeat for verification, but is a very accurate method.
I believe that original, and early replacement senders had "Delco Remy 12V Made In USA" and a series of stars stamped into the shoulder of the unit(just above the threads and below the hex).
If your sender is a late replacement, and does not have these markings, then chances are it reads too high (mine read about 30 degrees too high @ midrange), and required a resistor in series no normalize the readings.
If your sender is original/early replacement, then it probably reads too low @ midrange. This can only be normalized with additional shunt resistance in the temp gauge itself.
It sounds like your resistance reading of 785 ohms @ ambient is ball park, but what is ambient? The value will fluctuate significantly if "cold" means 50 degrees, or 80 degrees.

Joe

[Joe C.]

Re: Temperature Sending Unit

John:

The best way to verify accuracy of your sender/gauge system is to put the sender on a pot of water with a thermometer, hot wire it to your gauge, heat the water(very low flame to produce a slow rise) while monitoring the rise in temp. with the thermometer (known accurate) and compare to the gauge reading. This is tedious, and you may have to repeat for verification, but is a very accurate method.
I believe that original, and early replacement senders had "Delco Remy 12V Made In USA" and a series of stars stamped into the shoulder of the unit(just above the threads and below the hex).
If your sender is a late replacement, and does not have these markings, then chances are it reads too high (mine read about 30 degrees too high @ midrange), and required a resistor in series no normalize the readings.
If your sender is original/early replacement, then it probably reads too low @ midrange. This can only be normalized with additional shunt resistance in the temp gauge itself.
It sounds like your resistance reading of 785 ohms @ ambient is ball park, but what is ambient? The value will fluctuate significantly if "cold" means 50 degrees, or 80 degrees.

Joe

[Gary B.]

You can have your sending unit restored

John,

If you want to, you can have your sending unit restored by Fred Oliva in Florida. Fred also will work with you to check if your dash gage is working correctly. Fred is considered the best in the business for restoring Corvette fan clucthes and he recently has figured out how to do mid-year temperature senders. He cuts them apart and installs a new thermister, and then does some cosmetic restoration as well. You can contact Fred to confirm that he's still doing the temp senders at:

Fred Oliva
Vintage Automotive Research
2602 NW 94th Ave.
Coral Springs, Florida 33065
foliva@gate.net
(H) 954-344-2215 evenings

[Gary B.]

You can have your sending unit restored

John,

If you want to, you can have your sending unit restored by Fred Oliva in Florida. Fred also will work with you to check if your dash gage is working correctly. Fred is considered the best in the business for restoring Corvette fan clucthes and he recently has figured out how to do mid-year temperature senders. He cuts them apart and installs a new thermister, and then does some cosmetic restoration as well. You can contact Fred to confirm that he's still doing the temp senders at:

Fred Oliva
Vintage Automotive Research
2602 NW 94th Ave.
Coral Springs, Florida 33065
foliva@gate.net
(H) 954-344-2215 evenings

[Joe C.]

Re: You can have your sending unit restored

Gary:

Yes, I know Fred well. He is a good man, and truly takes the time to help others whenever he can. He is very busy now with a "new arrival", his day job, and his business.
He and I had a lengthy discussion about temp sender calibration, and he was very appreciative of the time and effort I spent in calibrating mine.
By the way, he is the only show in town when it comes to supplying new suppression capacitors for the directional flasher can.

Joe

[Joe C.]

Re: You can have your sending unit restored

Gary:

Yes, I know Fred well. He is a good man, and truly takes the time to help others whenever he can. He is very busy now with a "new arrival", his day job, and his business.
He and I had a lengthy discussion about temp sender calibration, and he was very appreciative of the time and effort I spent in calibrating mine.
By the way, he is the only show in town when it comes to supplying new suppression capacitors for the directional flasher can.

Joe