After much overheating on our recent trip to CO, and continued overheating even after replacing the fan clutch, water pump, thermostat, and heater hoses, I realized that the radiator was the culprit. I noticed some build up in the radiator when I emptied it when replacing the water pump.
New radiator in Fortuna: $550 plus tax. New radiator in Eugene: $420 with no sales tax. Hmm… I picked a new one up on the way out of the Oregon Country Fair and hauled it down on my roof rack to Eureka, CA. Thanks to Smalls who let me replace it in his driveway. It only took a few hours, but dang, that thing is heavy. Have a friend or a pulley if you do one that size.
I also added a transmission cooler. Knowing that my tranny temps were on the high side, and knowing that I was going to be hauling my horse trailer from CA to WA full of tools and building materials, I knew this was a good idea.
EDIT: Result of these upgrades: Hills I was overheating on driving up to Oregon Country Fair I flew up with no sign of overheating, even with my heavy horse trailer. The other funny thing is that my fan clutch started working. It never worked, so I replaced it in CO, and it still didn’t work. I think perhaps my radiator was so clogged with deposits that the super hot coolant was cooled by the time it got low enough to heat and activate the fan clutch (it is activated by heat coming off the radiator, which it sits behind).
Note to 7.3L IDI engine owners: get a copper/brass radiator, not an aluminum one (even though they may be cheaper). These engines NEED SCAs (special coolant additives) which help prevent cavitation (coolant slamming against the outside of cylinder walls repeatedly and wearing small holes in the cylinder wall. SCAs need to be put in a low silicate coolant (like Napa green). Silicates are put into coolant to protect aluminum parts. Therefore you’d have to have opposing chemicals in the system. There was one coolant (forget the name) that would work in this system, but I like to be able to have the flexibility to add any low silicate coolant in a pinch. Try SCAs like: NAPA Kool, DCA4, or VC8. Get test strips to determine how much you need to add.