Hi folks,

I experienced some engine temperature weirdness on a tow through AZ this weekend. The truck is a 2007.5 6.7 QC DRW 4x4 auto, with about 65k on it. I have towed with it for 6 years, a gooseneck race trailer that weighs about 15k loaded. Until this weekend, I had never towed with it in extremely high temps (previously, about 95 ambient was probably the highest). This weekend I towed from St Louis to LA on I-40, and everything was fine until I got to AZ. As we went further and further west, I began to hear the fan more and more as the outside temps climbed - no surprise. On one long hill in AZ, the outside temp was reading 108+, the fan seemed to reach a very high pitch, then suddenly shut off and the engine temp gauge instantly shot up several positions. In normal towing, it obviously is about a needle-width to the right of center. In hot towing, it was consistently holding about 2-3 needle-widths to the right of center, with the fan noise fluctuating depending on the throttle load and speed. When the fan shut off and the needle jumped, it was still not red, but about 2/3 there. It was very digital and instant when the fan shut off. I immediately backed off the throttle, and within 2-3 seconds, the temp gauge went back down, the fan kicked on again, and all was good. This happened two more times while in AZ, exact same symptoms, and all three times, as soon as I backed off, the fan kicked back on and the temp gauge went back to the "normal" hot towing position of 2-3 needle-widths to the right. I know that the temp gauges appear analog, but likely are assigned a range and a specific position to display. But what concerns me is that the fan seemed to almost "give up". The fan shutting off and the needle shooting to the right was too instant and exact for it to be the engine actually overheating that much, it was almost like the fan shutting off sent the computer a message to display the hot temp.

For the load I had on the truck and the speeds I was towing (65-70 mph), I am not surprised that I experienced some high engine temps. I am just concerned that the fan isn't acting normal, I don't understand why it very clearly "shut off". Anyone with any insight or thoughts?