I feel your issue is airflow. Not that I think I'm always right ha ha ha. I added some genright vents in my hood. You should have a negative pressure behind your rad. No issue when going slow with your fan running, but an issue at speed. Seems obvious to me.
From my last update post:
While it's not conclusive, I believe the bullbar, winch and led light might be creating a laminar boundary layer (air) in front of my radiator.
I don't really want to remove that stuff and I like my PS bumper a lot, so I am inclined to think about ways to alter the air flow at highway speed.
I will probably invest in genright louvers for the hood to both expel some underhood heat and, more importantly, to promote a lower underhood air pressure to affect the radiator flow.
I may also try an underbonnet or air dam below the radiator to keep air pressure behind the radiator from increasing due to turbulence of the under carriage.
I am convinced the air speed is setting up a bad flow potential in my setup and the fact I am boosted with an e-fan is taking this weakness to the point where it can cause overheat.
It is my belief that if I did all this at 55 degF or lower, the small active radiator area that I get at high speed might actually be enough to handle the heat and that could cause me to think my issue is solved. 65 deg. F was right on the border where 60+mph was getting me to overheat.
Think Jeeps have no Aero...? Think again. In truth, a conventional setup would not care about the aero effect, but that's not where I'm at.
Case closed for now on the cooling system, but more work is needed on my rig if I want to run 70 mph on a 90 deg. F day with A/C on! ...never turned it on in this test.
Remove winch and bull bar on a 70 degF day and see if I have similar overheat results (have to wait till warm weather )
Consider louvers on low pressure-high heat areas of the hood to promote flow
underbonnet/airdam (maybe one that I can put on just for driving and pull off for wheeling)
fabricate a giant ram air cone for each side of the winch to direct flow under the boundary layer (ugly, but the Mech E in me, would love to test that...)"
Wood, I think that comment is right in line with my experience so far.
I will probably do louvers first and then maybe experiment with underbonnet or shroud stuff.
I am reluctant to swiss cheese the fender liners right now because if the louvers really reduce my radiator pressure differential to promote flow, I don't want to disrupt the air flow between the radiator and louver exits until I get some data...
I'll add one more.... I cleaned my air filter to find I was pulling most air from my unblocked engine side (think higher IAT). I also think my exhaust manifold gasket is leaking a bit (higher underhood, heating up the stuff near the bank?) and the fuel pump doing lean at max load was such a great point it is worth looking at.