Troubleshooting & Installing Temperature Sending Unit '61 Dart Slant Six

[Razbo]

After two years, I've worked down the list of major to-do's on my Dart. The big one now is that my temperature gauge doesn't budge no matter how long the engine has been running. Today I used a tester to connect the temperature sending unit to the battery ground after running the engine for a couple minutes. My daughter watched the gauge slowly move off the cold mark. That should indicate that the gauge works. So I could replace the temp sending unit right away, but that may not be the problem nor solve it completely. I noticed that the temp sender appears to have been installed two years ago by the previous owner with Teflon tape wrapped around the threads. As I understand it, Teflon wrapped around the threads is an insulator that prevents grounding the unit. What should I use as a thread lubricant that would enable the unit to be grounded?

 

[Big_John]

After two years, I've worked down the list of major to-do's on my Dart. The big one now is that my temperature gauge doesn't budge no matter how long the engine has been running. Today I used a tester to connect the temperature sending unit to the battery ground after running the engine for a couple minutes. My daughter watched the gauge slowly move off the cold mark. That should indicate that the gauge works. So I could replace the temp sending unit right away, but that may not be the problem nor solve it completely. I noticed that the temp sender appears to have been installed two years ago by the previous owner with Teflon tape wrapped around the threads. As I understand it, Teflon wrapped around the threads is an insulator that prevents grounding the unit. What should I use as a thread lubricant that would enable the unit to be grounded?

Nothing.

It's brass pipe thread into cast iron. The pipe thread is tapered and the brass will deform slightly and seal.

 

[Razbo]

Today I had time to remove the old temp sending unit. It looked like the unit had a good ground with the block. Went to my bookmarked page at Advance Auto Parts to order one of the Carquest units that last week they had said were fits for my car. BTW, those sending units did not look like the units pictured at other parts sides, but they did look like the one on my engine. SURPRISE! When I went to order one of those Carquest units from Advance, the screen had a warning in red that said neither of them would fit my car! From looking at other pictures in the course of my search, they are different than all of the other pictures for a '61 Dart 225 six. Now for a possible wild card. The engine is a swapped-in rebuild. It might be from a newer model year. I'm going to check and see if I can get the build date off the block. I'm also going to try contacting the rebuilder, Joe Gibbs Racing. I'll update you on my progress.

 

[Razbo]

success? Maybe. Supposedly tracked down the proper temp sending unit for a later model slant six that looked a match for the one the car. Surprise...the major parts supplier substituted a unit its site said was correct for a 1961 block instead of what I ordered and they didn't inform me. Tracked down another match for my post '64 block and installed it today. Good news is that the temp gauge moved just to the right of the "C" mark, but only after running 4-5 minutes. Better than nothing. If the needle starts moving further in, that could be a warning. Next up is checking the resistance ratings for the unit I bought versus the ones that were OEM for a '61 block.