Make up a MECHANICAL CAPILLARY TUBE GAUGE. Interrupt the outgoing fluid from the transmission on it's way to the cooler. Use a threaded brass block with a "T" suitable for the gauge bulb. Double flared fittings on the tyranny line. Wrap the line from the transmission with fiberglass mat just like they use on body repairs. Four wraps. Then fiberglass resin.
This reads fluid temp as the transmission sees it. No other manner of reading transmission fluid temperature is valid.
Now for a question:
I use MoPar synthetic fluid in the toad because I have to. If Mercon or Dexron synthetic fluid is available, does it have a good enough user reputation to offer high temperature lubricity and resistance to breakdown? The stuff isn't cheap. MoPar claims life of transmission usability. Har Har. I have changed it twice in 90,000 miles.
But the longest lasting fluid operates at less than 100F. Use that as a sense of perspective. Engine oil on the other hand has both minimum and maximum limits because of combustion contamination boil-off and thermal clearances. I want to fit a tranny cooler to the toad. And a big pusher fan in front of the AC condenser.
My bus uses 50 weight oil in the Fuller assembles. I chose Lubrication Engineers because of extended lifespan.
