Did you ever hear the fan go full lock for a cool down?
And the life you describe sounds like it's in a field all the time. Which is not a good scenario when it comes to clogging up the cooling stack out front.
Not talking about what you see thru the grille, this grass and bug buildup will be sucked in from the bottom and collect/mat up on the fins, in between each coil, blocking the air flow thru the stack and to the fan clutch.
If the heat doesn't hit the fan clutch, it's not going to know the house is on fire and lock up full howl (which should immediately drop the ECT gauge).
clean the stack, then try to duplicate. Easiest way is to drain and remove the radiator, leaving the CAC in place.
It's a common thing to see after years of service.
Once you've verified the stack is clean and flowing air and the problem persists, If the fan never kicks in full lock, then look at replacing the fan clutch.
If at that point after cleaning the cooling stack, the condition persists and the fan is working, then look to the T-stats sticking open as a cause.
replace with new 180/185 set.
Going lower won't fix the problem and will make the truck use more fuel.
2007 LBZ 3500 LT3 DRW Crew Cab, Sulastics, Putnam XDR 15K, B&W 30K-Turnover GN+Companion, Ride-Rite Air...EFI'd by Rob
2008 LMM 3500WT DRW Crew Cab, 8 'Flat/GN, Workforce Alum Toolbox, Ride-Rite Air Use-ta Haves 2006-6.0 3500 WT DRW ExCab Flatbed, 2005-LLY 3500 LS DRW Crew Cab, 2002-LB7 3500 LS DRW Crew Cab I Live my life in such a way that when my feet hit the floor in the morning...Satan shudders & says "Oh shit, he's awake!"
Last edited by Hook'em_Horns!; 07-07-2019 at 05:53 PM.