98 24 valve overheating in stop and go traffic in B'ham, 93 degrees, pulling 10K fifth wheel. Fan clutch( original) with 170K miles not working so I put new Hayden, part number 02798, on. Guess what. It doesn'work either!! Temp goes over center mark a bout 1/8 inch. Any suggestions? At what temp is this thing supposed to lock in? Website says 170. that is BS.