A few years back, I was sending data to
Taco2Cruiser from a trail close to home that I could repeat from one day then go back up the trail another day with different type of fuel, fuel level, ambient temp, ect. The trail went from 5k feet to 9k feet up a rough mining road that would definitely shake the fuel in the tank the last 3 miles in low range and avoiding differential bashers on 33"s. The first five miles were just dirt FS road. The last time I collected data I was 5-6 miles in and about 85 deg and started smelling raw fuel venting from the vent behind the fuel fill door not the gas cap. Not boiling, just very dense fuel vapors. All of the cooling systems fins up front have been inspected, cleaned for the heck of it, inspected again with no fault found.
I can only say that from my data points collected that a higher ambient temp and engine load is what caused my system to vent fuel vapor. Fuel type or volume at 50% or 90% full didn't matter. Also, a tail wind doesn't help the cooling system and makes the cabin smell like fuel and does not build confidence with any passengers or pedestrians.
I started to look for a OEM fuel cooler and found the same ones sr5pickup found. I do not have a shop any more or a lot of room in my garage so I have hesitant to find a place to install a fuel cooler with a fan up front.