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Thanks for the reply Mark. I have a 1996 Class A Motorhome built on a F53. I recently had the radiator replaced and the it worked fine as long as it was just idling. However, once I was on the highway within 5 miles the temp gauge would rise to the high end of normal. I replaced the theromstat, fan clutch, gauge sensor & hoses and no luck. On the last test drive the transmission lost all the fluid out the bottom of the bellhousing. The transmission has been replaced but I have no taken it for a test drive as of yet. The water pump has not been replaced (42000 miles) because I thought if it did not heat up at idle the pump should be ok.
I would think that if the transmission is overheating so much, it would be cooking the fluid as well. See if the fluid is burnt. But it sounds like you have a cooling issue with the engine.
Start checking the simple things first; see if the radiator is clogged. If you can get at it, feel the core while idling to see if there are cold spots, especially at the upper tubes. That usually means they're not flowing coolant, which should be hot coming from the engine.
Then open the cap to see if there are bubbles coming out, or if you smell fuel or combustion gasses. That usually means a blown head gasket. That's usually accompanied by coolant gushing into the overflow tank.