78 440 Nitro temp sender?

[Nitro208]

I've "vacationed in my garage" for the last 2 years fixing up and restoring a 77 turned 78 Nitro with the Xenoah G44BW. Just got the old girl running last weekend and I'm curious if anyone has any input to assist me in resolving an issue with the temp gauge not working.

Information as follows.

- Full coolant, plenty of warm up time checked with a thermographic camera using black electrical tape on heads, and hoses for correct temp readings. I should have got something on the gauge. 
- 14.3 volts AC constant through out rpm ranges (not positive what nominal should be on these voltage regulators)
-Green wire from the gauge is hooked up to the sending unit, and continuity checks out. There is a 68.5 Ohm resister already wired inline, and the cable reads 70 Ohms from gauge to sending unit when disconnected from both)
-I've checked continuity on the circuit board, to the gauge,and went through all of the other wiring harness circuits. Lights/ controls work, ect.
- Checked the gauge by removing the green wire from the sending unit and taking it straight to ground. The gauge needle steadily climbed to full hot position. (I'm thinking this means the gauge is good)

I guess my thoughts at this point are directing me to the temp sending unit. I have it removed and it seems to respond to changes in temperature if I put an ohm meter across the two ends. I'm just not sure what normal values should read.

If anyone has any resistance values, or can think of any other ideas please chime in. I'm also not opposed to replacing the sending unit if I can find a new one that will work. (The old one is marked NS 8P, but I cant seem to find it online)

Last,  thanks to everyone that has added info to the board in the past. I've been reading throughout this entire project, and couldn't have gotten this far without everyone. In fact It's been fun running into issues and finding a lot of the solutions here with you all. I plan on doing a write up with pics once i get her finished.


Thanks, 208

[Ruppsforever]

Is it warmed up enough to get the bumper and radiator warm ??

[Nitro208]

Yep the bumper and radiator were both warm

[Nitro208]

So I've ordered a new temp sender TS111. www.summitracing.com/parts/smp-ts111 I found it referenced in some random posts about it being compatible with the Nitro's. I know the threading fits, and I've checked resistance across my old sender unit and the new one. Old sender resistance at room temp (cold) around 650ohms, and at boiling it drops to 35 ohms. The TS111 reads about 700ohms (cold) at room temp, and drops to 25ohms when boiling. They are fairly close and respond similarly when heat is added. This makes me think that the old temp sender is still good.
I'm wondering if the old sender lost a good ground connection through the threads to the head of the engine. I found some sealant in the threads, and I'm going to clean it up and do another test to see if this is the issue. I know it worked 20 years ago, but I bet we've all said that before.

I'll post what I find.