I also wonder if your thermostat isn't opening fully.

 

My bet is still the fan clutch, but the thermostat was also replaced with a new Motorcraft unit so anything is possible.

It behaved fine running at 70 mph east across Wyoming on the fast stuff. Probably wouldn’t even need a fan I am guessing if you’re ramming 40* air into the cooling stack at that speed. It also tolerated some pretty good climbs without the temps getting out of control, but obviously when you’re down to 35 or 40 mph in 3rd gear pulling a long nasty one with a 12k trailer, oh yeah, the fan becomes critical then, so that’s why I am now officially sorry I didn’t get the Motorcraft clutch. Never had an overheat even in hot summer weather with that old one. DID have a pulley wear down and start slipping and making the belt squeal, but a new pulley fixed that.

I sat there for 3 hours until they showed up. Dumped 4 gallons of coolant in and it fired up and behaved fine the last 100 miles to Colorado. No tough hills though. I will say If you see EOT climbing up past 235*F or start to smell coolant, you better pull it over and idle it down NOW unless you want to spray $80 worth of coolant all over. It needed more top off when I got here too. So more like 4.5 gallons it puked.

 

I pulled it out and cleaned it off when all the new parts when on about 18k ago. It was totally plugged up, but the old clutch was stuck on, so it never overheated.

 

the bolt washers that attach the fan to the clutch will leave a scuff mark, so unless it’s a brand new fan it’s pretty easy to notice which way it goes back on by the imprints the bolts left. Also if it’s blowing air towards the engine that proves it’s sucking it through the radiator right? If you had it on backwards it would be sucking from the back and blowing towards the radiator wouldn’t it? I am pretty sure mine’s on right but that definitely caught my attention when I put it all back together a few months ago .

 

I have heard of 7.3’s that overheated and lived to tell about it. 6.0, yeah…One garbage fan clutch and one stupid operator and you just bought yourself a $10,000 engine rebuild probably

 

Going to back off my position that the fan clutch was the problem. It kicks on during a cold start and unlocks after 5 minutes or so of high idling to warm the motor up, so at this point I'm doubting it had anything to do with either the clutch, t-stat, or the belt slipping. Cap might have had nothing to do with it either. Externally the front the of the rad is clean (after I cleaned it recently), but crawling around under there and feeling the front of it (as best I could) after pulling over into a rest area a few days later, I seem to have cool spots on it, indicating it's got plugged up spots inside it and probably just needs a new one after 200k miles.

I did also notice the A/C condenser is pretty jammed up with crud, so that probably ain't helping, but I'm going to do something about that next week with the Lisle radiator genie tool. I also drained a 1/2 gallon out of the bottom and poured 2 of these in along with 8 oz of VC-8 to replace what was lost there, then topped the bottle back off. Maybe a couple of these massages along with staying back east here where the terrain isn't nearly as truck busting will help delay the inevitable radiator replacement. Cold spots on the rad and a jammed up AC condenser could affect the fan from working if the hot air isn't blowing onto the bi-metal coil and giving it the bat signal do something, is my thought.

 

You might have nailed it here. Pulling a travel trailer down to Kentucky last Sunday afternoon it was running a little too warm again IMO in mostly flat (some hills around Cincinnati) and not a hot day. I pulled into a rest area and popped the hood with the oil temp still at 216. Upper rad hose was very soft giving it a squeeze. I thought ah-ha, it must be a bad t-stat because it should be fully open at that engine temp and that upper hose should be very firm. So I swing by the Ford parts counter on the way back and get a new one and install it yesterday. Nothing seemed out of sorts except for that t-stat housing bolts were pretty loose which I immediately noticed. I put it all back together and have taken it for a couple of 15 mile or so test drives, and it does seem to be running cooler, but it's hard to say for certain on such a short test drive without a trailer if anything really got fixed or not. It's not easy to put enough load on the cooling system on a short-ish test drive to really know, but I was seeing oil temps of 210-212 driving empty 65-70 mph on the way back, which to me is higher than it should be. On the way down with the trailer I was seeing 220-225 which started to alarm me a little on the high end there a few times. I could tell something wasn't quite right.

I'm curious now if I had a bad/lazy t-stat compounded by a system that wasn't holding pressure correctly. Is it possible a system not holding pressure could cause the t-stat to not open and pressurize the upper rad hose? I don't know. It goes to the A/C guy Friday. While it's there I'm going to see if he can throw a quick pressure test on the cooling system. That's probably where I should have started. So round and round I go with this one. Frustrating.

 

If your hose is soft, you need a new radiator cap. Pressure is not building and you need it to prevent boil over when you need the cooling system the most. Or pressure is getting out somewhere else, but that would usually show up as a coolant leak.