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Flat ground or going vertical, wind speed and surface area doesn't change. I wasn't looking at the thermo transfers, purely the wind speeds. The wind on it's own exceeds the speed a fan can move it. Of course a spinning fan vs a stopped fan, the spinning fan will have less drag/resistance, so maybe that's why the fan kicks on?
Yea, I don't take too much from the racing world since it's a different environment. On my corolla I blocked off the upper grill, and around 70% of the lower grill. The opening for air was around 6in wide and 4in tall and never had overheating issues.
If the fan was so critical for normal operation, then blocking off the grill would cause more overheating problems even with the fan. Of course blocking it off completely would cause overheating problems, and that would be quite a test to try out. Block the front completely (as best as possible) and run on cooling of only the fan to see if at express way speeds (75mph) the vehicle runs hotter or not.
Generally speaking, wind resistance is a greater force to overcome than a hill, of course combine both and it takes even more power. I haven't done the math to see how much extra power is required to continue at the same speed up a given slope but 5-10 times seems a bit excessive. You can't measure the power based on how much throttle you give it, engine rpm is a major factor in HP output, atleast as I understand it. A lot likely depends on total weight of the vehicle too since a light vehicle has a much larger % of load being purely wind resistance while a semi truck has a lot of rolling resistance and the raw fight against gravity on a hill. I wouldn't be surprised if a semi needed 5-10 times the power to go up a steep hill and keep the same speed vs flat ground.
Anyway, hopefully I'm not coming off as trying to fight you or anything. Just some of the statements go against my experience. It would be interesting to read more up on the subject that keeps things in check, like using the math for the physics and accounting for the hill vs flat ground etc.
I did read that the 7.3l trucks temp gauge has an extra resistor inline with the sensor so it reads colder than normal. From what I read people speculate that with a big load it would push into the hot area and could spook some owners so they opted to lower the reading on the gauge. On mine, it runs about 1/4 the gauge lower than the middle "normal" spot and people say the gas trucks run dead center.
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