V10 Overheating - Fan Not Kicking-in

[DFord]

The first time I had my motorhome on a trip the fan clutch worked great. The temperature gauge would start to go up and the fan would kick-in (there's no problem hearing the fan kick-in, that's for sure!) run a little bit and kick back out, just like it should. Late last summer when the temperature was above 90F, the temp gauge would go almost all the way up very quickly before I'd catch it when I was using the dash air and going up hill. I found I could turn off the dash air and the gauge would drop back to normal. This happened several times to me and I've heard of several others having these same symptoms over at the RV.Net forum. No one seems to know what the fix is for this problem and I hoped someone this forum might know one. I know the fan clutch still works because I got it to kick-in over the winter while I was letting it idle to circuit the oil. As I speed-ed up the engine just before I shut it off, the fan came on strong and shut right off right away when the cold air got to it.

Anyone got a fix for this problem?