We have had our '99 HR with 5.9 Cummins and rear radiator for over 5 years and never had a heating problem. Saturday, while pulling our car over Seven Mountains on Rt 322 in central PA a warning buzzer came on. I glanced down and saw it was a temp problem. The hill is a three mile 7% grade with two lanes up and two lanes down. I have pulled this hill many times without a problem. I pulled as far right as I could in the right lane and stopped. I got out and checked the coolant tank and the fan. All was OK. We sat there for seven or eight minutes and the temp gage came down below the half lway point. I still had nearly a third of the hill to go. Watching the gage, we proceeded to the top. Just as we started to level off at the top the buzzzer came on again. Here there was plenty of room to pull over so we let it cool down. We continued our journey and had one more over heat incident on I 80 near Jersey Shore where I had to pull off. Buy keeping the RPMS up (manual shifting of the tranmission) we made it the rest of the way with out triggering the alarm but it ran in the red several times.
Yesterday before starting home I sprayed the radiator and condenser with a detergent. While underneath I saw a leaf sticking out of the 3/8" wide slot between the radiator and condenser. I looked in the opening with a flashlight and it seemed to be filled with leaves. What a screw driver and wire I spent an hour pulling the leaves out of the opening. Once the leaves were out I sprayed between the radiator and condenser with my detergent. I had Gwen start the engine and I played watrer on the fan and radiator until no more soap suds came out. That must have taken another hour but I didn't want to leave any of the detergent residue in the radiator to trap dust.
By then,of course, I was soaked and filthy so I took a shower and started for home. The engine ran cool all the way, never getting above the half way mark, even on the toughest pulls. A bonus from this is the AC seemed to run cooler than before. I guess it wasn't breathing either.
I know this is long winded but just wanted to point out something most of us probably don't consider when doing our maintenance. I will check that area with a flashlight from now on.
Bob K from PA