I found this thread after some "Googleing" and am hoping for some input on wether I should be dropping coin on a diagnostic mechanic or if there's something I can try to diagnose first.
Back in mid-June I drove my '04 F250 6.0 diesel 4-door 500 miles from home down to S. Carolina. It was a 9 hour drive time including a couple of pit-stops. Only one passenger on-board and no freight or towing. We stayed a night and the next day in SC and headed back towards home after dinner.
On the way home I started running the interstate pretty hard hoping to cut an hour off the trip. The windows were up and the A/C on to quiet the cab and it was then fan started briefly spooling up and down when I'd pass already fast moving vehicles. As the phenomenon is pretty loud and it'd never before happened it kinda' set me back in the seat and after checking the factory gauges for signs of trouble (none) I began nursing it at 75MPH or lower (75 mph = just about 2100). The fan activity ceased and I hadn't heard it again 'til yesterday when I ran the same trip with 2 passengers and a bed full of household cargo. I wasn't 45 minutes down the road when the fan began cycling for longer and longer periods at engine speeds above 2000 rpm. Again, no sign of trouble on the factory gauges. I stopped and topped less than a quart of coolant. I noticed then there was no pressure on the coolant cap when it was removed hot. I didn't hear from the fan for another couple of hours when it cycled briefly once or twice. By the time I got all the way down the road (8 hour drive time) the fan wanted to run almost constantly above engine speeds of 1750 rpm (65 mph). Between local stops and in-town driving the truck had maybe 3 or 4 hours intermittent down time before I headed back home with 1 passenger and an empty bed. The fan immediately started cycling constantly for brief periods - maybe 40% off 60% on at engine speeds over 1750 rpm. I ran under 1750 rpm ( 55-65 mph) all the way home through several extended stops - this time over something like 14 hours, with only a couple of brief fan cycles. I stuck an electronic thermometer in the coolant resovoir within 90 seconds of hitting the driveway (again no pressure on the coolant cap) and watched it track from 213 to 195 in less than a minute at engine idle. Thoughts on where the problem might lie or how to pin it down? I gotta' go back down the road in a couple of weeks.

 

My opinion on this, based entirely on what I have read on here and my own experience - so take it with a grain of salt, is that there is no answer to this question. That's not to say that I don't think something may be wrong, but I suspect trying to identify exactly what is wrong would be a very expensive and time consuming process, one which I am very certain Ford would not have any part of, especially if it is a software glitch. How are you going to show them or mimick the problem - take them on an 8 hr road trip!!!!

I would be interested to hear back from guys running the SCT setup if this issue goes away?

Higher or lower RPM's dont seem to make any difference with mine. During summer the fan is often on when I first start the truck and stays on for a few minutes.

 

I think you do have a problem but what it si I am not sure. Like heavy said it could be a glitch with the software progamming in the pcm. I ran today almost 200 miles with the 4k loaded boat in tow and the fan only came on once or twice and just for a short low speed event. I havent had time to get the guages orderd or installed yet but the temp guage, uh glorified idiot light, never moved from its normal spot. So I am confident that I dont have a problem. Oh yeah it was about 92* here today, I had 4 passengers too and the A/C was maked out.

I would see if there are any codes in it, maybe the fan switch is bad. OIf nothing there see what flash you have in the PCM. Good luck.

Sarge

 

I will give you my experience, take it and use it as you will. My 04 crew cab ran flawlessly for the first three years. I pulled a 31' WW toy hauler in Arizona. My fan never kicked on until I was towing and climbing. When not towing it never came on in town or freeway. One day I heard it kick on in town and thought what the hell, as it had never done this before. It began doing it regularly so I took it in. Turned out my EGR cooler was leaking. No other sign but the fan kicking on. Had it replaced under warranty and have not had an issue with the fan since. I would hate to see you take off on your trip and have something go wrong.