im having overheating problems at high speed/high rpm/under load. the only codes ive gotten are EGR dpfe (0401) truck is 99 f250 with the 6.8
new egr valve, dpfe, new coolant, new thermo, new sensor under manifold. I blew 90 lbs air pressure thru the egr lines, big and small, they were clear.
so whats left? I never hear my fan clutch......should I? ive had other trucks and the fan roared when first started for a few seconds, and then again when you were hot...they really roared.
is it possible for the egr port where it goes into the throttlebody to be plugged? guess I should've checked that when I had the egr off.
would an aux. fan be a waste of time?


any ideas guys? any and all help is much appreciated.


edit: this is pulling a 3500 lb camper trailer up moderate hills.

 

I should add that there is no spewing or loss of antifreeze, no limp mode, and since changing everything out, no CEL or codes. I do get a small light ping though.

 

Have you changed the thermostat? It would be one of the places I would start. You can check it by letting the motor warm up. Then grab the top radiator hose to see if it's as hot as it should be. If its hot than the T stat is open and water is flowing if the hose is cold than thats the problem. Also to check the fan. With the motor off assuming you dont have a electric fan grab the fan and give it a spin if it keeps rotating than the clutch is bad. Make sure that the fan doesn't wobble. If it does the clutch is shot.

 

you should be hearing your fan roar for a few seconds at start up. if you arent, the viscous clutch has failed. Your past experience is a good indicator of how they are supposed to work.

start there and see if that helps.

 

the thermo(stat) is new, motorcraft. that was one of the first things I did. the fan has resistance, and by no means spins free...but I think that definitely might be the problem, cuz I never have heard it even when the gauge is pegged hot.

 

Ok get the truck up to running temp. Have someone shut the truck off. Watch the fan and if it just spins freely than the clutch is bad. if it stops in a reasonable time than the clutch is bad. The fan should stop fairly quickly. When driving down the road with a bad fan clutch there is enough wind coming through the radiator to make the fan rotate backwards. Don't just throw parts at it until you check things out. I would check the hoses anyway because I have seen new parts not work.

 

just checked the fan as you said....it stops almost immediately.

 

The tests above are nearly worthless in all cases. I've had bad fan clutches that easily pass the "stops right away" tests.

The best way is to listen when you start your truck. If the fan doesn't roar for the first few seconds it's bad. Same thing goes when the needle comes up on the gauge, if the fan doesn't howl the clutch is bad.

I dinked around with chasing down overheating problems by erroneously diagnosing the fan clutch as good enough times to realize that all it was, in the end, was the stupid fan clutch anyway.

Not trying to discount anyone's opinions, but based on my experiences your fan clutch is bad and that's where id start.

 

thank you for all your input.....when I finally get this I will make sure you all know what it was......in the meantime im not just scratching my head wondering what I missed.
the upper hose does get hot, and when the truck is HOT, the expansion tank is quite a bit above the max line......like half way to the top.
.I have it just under max line when cold

 

How fast are you moving when the truck overheats? What was the ambient air temp?

I've pulled my 3,500 lb boat with my old Lincoln Town Car for one full summer without a cooling fan. I removed the clutch and fan completely, and the electric fan wouldn't engage until the ECT got above 220°. That never happened unless I was in stop-and-go traffic. I could pull that boat up and down any hill I wanted without that happening as long as I was going above 40 MPH. The OP's Super Duty has a MUCH larger radiator than my Lincoln does.

I'd look more towards a partially obstructed radiator or eroded water pump vanes. How well has the cooling system been maintained?

 

temps in the upper 80s to mid 90s. if I keep it under 60 itll stay in the normal range. hills or higher speeds/rpms get me to peg hot. this is without the AC on, and with the overdrive turned off.
ive flushed the radiator and washed out all the bug guts from the front. water flows thru easily.
my small scan gauge shows ive hit 225*

 

225 isn't terribly hot. You're getting an overheat indicator on the gauge at 225?

You shouldn't see 225 with that little trailer though. I pulled 16,000 lbs across the country with my old Excursion and never saw over 210. How well has the cooling system been maintained? Has it been changed every 30,000 miles? Might be time to pull the water pump and see what the vanes look like.