It is claimed that 1/8" Viton hose is best for the injector return hoses. I just put on my 1985 300D because the woven hoses were leaking pretty bad (~4 yrs old, but using Diesel HPR). I bought 10 ft for $19 on ebay from China. Can't tell if truly Viton, but has held up for 2 weeks so far. I tried a little silicone hose and it started swelling and leaking in 2 days.

I also have seen the dash gage go high after a coolant change, even pegging at 120 C. But, I don't think the whole engine got so hot. I think when you have an air pocket, the sensor sees hot vapor. Once I added more coolant (tank had dropped) it ran OK. If you installed the thermostat correctly w/ the little vent hole up, the air should eventually purge out, assuming the little copper rattle pin move freely to keep the hole open.

You could test the clutch-fan like Ed China did on Wheeler Dealers. He grabbed it on an idling engine w/ a leather glove and said if it was good he wouldn't be able to hold it. The true metric is to count your fingers before and after this test and subtract. 5 missing fingers = excellent fan clutch.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans