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My Ranger has the grille totally blocked, but it also has openings below the bumper and a fairly large gap between the hood and grille without any insulation between the two.
Fan clutches usually run between 1500 and 2500 RPM depending on the temp of the air coming through the radiator. I seldom use the AC in the truck and have seen no rise in gauge readings.
You can actually hear the fan clutch when it is fully engaged, the fan noise will be significantly higher. In a lot of vehicles you will hear the fan running at higher speedds when you first start the car, then it starts to let the fan clutch "slip" more and fan noise is reduced.
The higher the coolant temperature (within reasonable limits) the better your mileage will be as long as you are not seeing a significant rise in coolant temperature. As long as you have a 50/50 mix of coolant the temps can get to 220 without any problem. In fact Mercedes bulletins stated that 256 degrees was not an issue with their diesels back in the 1980s but I would not like to see that temp level under any conditions, that was their maximum allowable. Not sure if it would apply to other cars.
When the fan clutch is worn out then you get problems. I used to show people their bad fan clutches by stopping the fan and spinning it backwards WHILE THE ENGINE WAS RUNNING! This was on the old Datsun-Nissan Z cars and there is NO WAY I WOULD RECOMMEND ANYONE TRYING THAT!
regards
Mech
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