I too have had what looks like overheating problems with a Cummins ISL 400 in a 2006 Newmar Dutch Star on a Spartan chassis. Temperatures on the Jellico Pass of I75 would run from 195 up to 235 on the dash gage.Then we blew a hose from the engine at the HydroHot system. This hose was by Newmar. We replaced both the in and out hoses with quality hose and added a shut off valve back at the engine so if there was ever another problem we could isolate the HydroHot. I'm heading out again for the Jellico Pass 9/15, we'll see what trouble I find. Davis reports there is a bulletin on a radiator hose location fix and I will be following this as I know we've had no radiator service. BTW, Cummins tells me that 195 to 225 is normal - my car doesn't have this wide range!
Fred Leport
Union KY
