2002 Ranger -strange overheating problem
I have a 2002 Ranger XLT pickup with an auto transmission and a V6 3.0 engine with 66,000 miles on it. The truck runs fine does not use any fluid, oil or water, no leaks and no water/antifreeze has been added. I live in Eastern NC which is extremely flat and the biggest hill we have is a highway overpass. The vehicle has absolutely no problem in this area, recently I have been running to the west side of the state which is mountainous. As soon as I run into a grade of 5 to 7 degrees (US 40 in Ashville NC) the engine temperature starts to rise to the point that I have to slow to 40 mph to keep it from going into the red area. The vehicle does shift out of overdrive and steps down in gear as the grade increases. As soon as I crest the grade the temperature will slowly go down. Belt has been checked, radiator cap has been changed and thermostat replaced. I have taken it to my local Ford Dealer (flat country) and they can find nothing wrong. To duplicate the problem I can hook up my boat trailer and take it out on the highway and the truck starts to over heat. I have towed my boat and climbed mountains with this vehicle for over 5 years and never had a problem until now, of course the dealer doesn’t want to hear this . Any suggestions?