It might be a good idea to have your cooling system checked to see if the coolant is sufficient and that the radiator is functioning properly. Most rigs with the 8.1L engine ALSO have electrically operated fans in front of the radiator that provide cooling when temps get too hot. All of the fans must operate properly to keep things under control, especially in hot weather. The mechanical fan clutch, which causes the roar, does occasionally go bad and needs to be replaced. If the temps are continuously running too hot, for no obvious reason, it is time to get things checked.
