Some of you may remember a 9-page thread from around Aug. where I thought I was having trouble with my motor running hot. Turns out it was running at perfect temp but the Wells TU5 temp send unit I used to replace my original one was reading 30-40* too high.
After all the posts on here and CF I learned that high reading are very normal on pretty much ANY replacement temp sender unit, including most of the newer ones that are sold as "correctly calibrated".
About the only solution seemed to be digging up an original temp sender unit that still worked. Most of the Chevy SB through the late 50's and 60's all used basically the same units with only slight differences whether the car had an actual temp gauge or just a warning light.
Trying to dig up an original unit was harder than expected though. Tried all the local junk yards and salvage yards and was basically laughed at when I explained what I was looking for.
Tried again with a few phone calls the other day and at one place was told 'yep, we got one". I ran over and what he tied to say was an original NOS part sure didn't look like one to me. It was lacking all the proper markings and the dimple on the probe end. I explained it was wrong and was about to leave when he told me to try another guy.
Turns out this other guy works on '55,'56,'57 Chevy's as a hobby. I went to his home and in his six car garage he had a '55 Nomad in show condition, a '57 Belair in show condition, another '57 Belair he was rebuilding, a '36 Plymouth Woodie, and a few more cars under covers.
Best of all he had two full drawers of old original temp sender units of all types. After sorting thru them I found two that looked correct and bought them off him. He even said if they don't work I can return them to him.
I checked them with my multimeter and the impedence level was MUCH, MUCH closer on both units to what it should have been than what my old orininal unit is giving me (no surprise since it decided to quit working right) and closer than what the wells TU5 is giving me.
One of the units in partivular seems like it may be right on or very close to ideal.
The proper impedence reading at an ambient temp of 75* would be 700ohms. The impedence readings should decrease as the temps go up and of course also increase if the temps go down. I got a reading of 655 on one of them but that included my finger on the meter's probe tip holding it onto the surface of the unit and my finger would raise the temp slightly so the lower reading should be normal because of that.
Once my carb gets back and I can run my motor it will only cost me a couple quarts of coolant to check each unit in the car but I have a good feeling on this one that I may have found at least one unit that will give me an accurate reading on my gauge. If both units are good than I'll have a spare to keep.
After all the posts on here and CF I learned that high reading are very normal on pretty much ANY replacement temp sender unit, including most of the newer ones that are sold as "correctly calibrated".
About the only solution seemed to be digging up an original temp sender unit that still worked. Most of the Chevy SB through the late 50's and 60's all used basically the same units with only slight differences whether the car had an actual temp gauge or just a warning light.
Trying to dig up an original unit was harder than expected though. Tried all the local junk yards and salvage yards and was basically laughed at when I explained what I was looking for.
Tried again with a few phone calls the other day and at one place was told 'yep, we got one". I ran over and what he tied to say was an original NOS part sure didn't look like one to me. It was lacking all the proper markings and the dimple on the probe end. I explained it was wrong and was about to leave when he told me to try another guy.
Turns out this other guy works on '55,'56,'57 Chevy's as a hobby. I went to his home and in his six car garage he had a '55 Nomad in show condition, a '57 Belair in show condition, another '57 Belair he was rebuilding, a '36 Plymouth Woodie, and a few more cars under covers.
Best of all he had two full drawers of old original temp sender units of all types. After sorting thru them I found two that looked correct and bought them off him. He even said if they don't work I can return them to him.
I checked them with my multimeter and the impedence level was MUCH, MUCH closer on both units to what it should have been than what my old orininal unit is giving me (no surprise since it decided to quit working right) and closer than what the wells TU5 is giving me.
One of the units in partivular seems like it may be right on or very close to ideal.
The proper impedence reading at an ambient temp of 75* would be 700ohms. The impedence readings should decrease as the temps go up and of course also increase if the temps go down. I got a reading of 655 on one of them but that included my finger on the meter's probe tip holding it onto the surface of the unit and my finger would raise the temp slightly so the lower reading should be normal because of that.
Once my carb gets back and I can run my motor it will only cost me a couple quarts of coolant to check each unit in the car but I have a good feeling on this one that I may have found at least one unit that will give me an accurate reading on my gauge. If both units are good than I'll have a spare to keep.
