Interesting, I have a 2005 Mandalay 40B with a CAT C7, 350 HP, side radiator as well. I have 34,000 miles and am second owner of coach, since 20,000 miles. My engine overheats just as yours does and even when not towing. I live in Vegas and it heats up in the same pass as yours, I try to run at 2000 rpm to stay cool. I have just returned from a trip to Austin and had overheating problems the entire way. I have it at the CAT dealer now being inspected and have heard of all the remedies that are listed, clean radiator, hoses, belts, etc with no success. Will post results when Coach is returned from CAT.
