I dont live in the desert either, I was just giving you a worst case.
No matter what I tried, with a 4.0L, 4.0L HD radiator, full shroud and e fan in 4 low it would eventually heat up.
Just my experience with my BII
I learned MANY others on this forum suffered similar results when trying the e fan
So I guess the best advice for a trail righ with e fan is approach with caution
A factory like cooling system with an e fan just may not be adequate enough, but I am sure its hit or miss as we all know cooling system setups vary. What works for some may not work for everyone, I guess I jsut gave up on the e fan after 3 failed attempts
FYI it would never run hot during normal driving or even 1/3 of the day in 4 low, but eventually it would get to a point (like 225 degrees water temp) and then never come back down, heck most of the time around town driving even with the AC on the e fan would never even kick in and the truck sat at 190 degrees (I had a 180 thermo back then), but sure enough hit the trail, go slow enough and BLAMO it would start to get hot and keep climbing, every time in the colorado mountains (yes yes we lack oxygen, wonder if that contributed?)