cseby

put a new cummins thermostat (#3802968) in my 1990 d 350.it will start to put out heat about 3 miles down the road.put the same cummins thermostat(#3802968) in my 1989 d250.it will not start to put out heat for about 12 miles.both are installed correctly.both heads have been cleaned up with a die grinder as per dodge service bulletin.what's the problem with my 89? this has bothered me for the last two weeks.i can't come up with an answer.

1992gen1_fan

You'd just have to test the thermastats side by side and see which opens first, but all i can think of is maybe the one in the 89 might be a dud or somthin. i know my 92 used to take a long time to heat up and changing thermastat fixed that.

wannadiesel

I'd try a different thermostat. They seem to be quite inconsistent.