This help? found this out of my Service Manual.
Fan Clutch Test

Spin the fan blade (8600) by hand. A light resistance should be felt. If there is no resistance or very high resistance, the minimum and maximum fan speeds must be checked as follows:
Fan Clutch Test—Minimum Speed Requirement

Use a suitable marker to mark the water pump pulley (8509), one of the fan blade retaining bolts and the crankshaft pulley (6312).
Connect a tachometer to the engine.
Install a throttle adjusting tool.
Connect the Digital Photoelectric Tachometer.
WARNING: To avoid the possibility of personal injury or damage to the vehicle, do not operate the engine until the fan blade has been first examined for possible cracks and separation.

Start the engine and run it at approximately 1,500 rpm until the normal operating temperature has been achieved.
Operate the strobe light at 4,320 rpm for 5.4L and 6.8L engines and 3600 rpm for 7.3L diesel engines, and aim it at the water pump pulley. Adjust the engine speed until the light flash and the water pump pulley mark are synchronized.
Aim the strobe light at the fan blade bolts. Adjust the strobe light until the light flash is synchronized with the marked fan blade bolt (the fan blade appears to stand still).
The fan blade speed must not be greater than 1,900 rpm on 5.4L engines and 2,000 rpm on 6.8L and 7.3L engines.
Turn the engine off.
If the fan blade speed was greater than 1,900 rpm (on 5.4L) (on diesel engines and 6.8L, 2,000 rpm), install a new fan clutch (8A616).
Fan Clutch Test—Maximum Speed Requirement

Perform Steps 1 through 5 of the Fan Clutch Test—Minimum Speed Requirement.
NOTE: The temperature of the air hitting the fan clutch should be above 96°C (205°F) for maximum fan speed.

Block off areas on each side of the radiator in the engine compartment and the front of the radiator grille (8200). This will raise the temperature of the air striking the fan clutch and should cause the fan blade to operate at maximum speed.
Place the climate control function selector switch in the MAX A/C position and the blower motor switch in the HI position.
Adjust the strobe to 4,320 rpm for 5.4L and 6.8L engines and 3,600 rpm for 7.3L diesel engines.
WARNING: To avoid the possibility of personal injury or damage to the vehicle, do not operate the engine until the fan blade has been first examined for possible cracks and separation.

Start the engine and adjust the engine speed until the strobe light flash and the water pump pulley mark are synchronized.
Aim the strobe light at the fan blade retaining bolts. Adjust the strobe light until the light flash is synchronized with the marked fan blade bolt (the fan blade appears to stand still).
If the fan blade speed is less than 3,600 rpm on 5.4L engines and 3,500 rpm on 6.8L engines, 2,850 rpm on 7.3L engines, install a new fan clutch.

 

Aside from all the formulas I don't understand, I agree with these statements. As appreciative as I am to have received suggestions and information from all, this is one that I would have liked to have been told "It's a popular mod, but research it for yourself and make an informed decision on if it's right for you." Rather than "This is a cheap, easy mod, and one of the first things you should do."

 

Thanks a lot I filed away your entire post for future reference and listed the pertinent parts above which confirm my use of a 205 F ECAT for when the fan clutch locks up. Now I'm wondering just how a 170 F ECAT for when the fan clutch drops back out of full lockup got into my head? It seems to me there should be a spec and a test for that just to make sure the clutch is releasing as it's supposed to after the high-speed mode has done its job and cooled the engine compartment back down to some temperature that Ford deems to be acceptable.

Now does anyone have an estimate as to how many cubic feet of free air space is available in a 7.3L engine compartment from the hood (closed of course) down to the bottom of the engine? I can no longer go look under the hood of my F350 but lets assume it's 5.28 ft^3!

A 5.28 ft^3 engine compartment air space implies that an "open element" AF which is sucking 528 CFM to supply the engine sucks all of the available air out of the engine compartment 100 times each minute! Where does all of the needed replacement air come from?

It comes from the ambient air but thanks to the Ford design 100% of the ambient replacement air is forced to flow through a 140 F A/C condenser, then if you're at a sustained 18 psi boost it's forced to flow through a 160 F IC, and finally it's forced flow through a 190 F radiator, and then it picks up even more heat from the exhaust manifolds etc.. and then it flows directly into your "open element" AF!

And yet people continue to claim that the air flowing into their "open element" AF is only 2 F or 20 F or whatever unbelievable (for me anyway) low number of "F" hotter than the ambient air is!

Now consider an alternative. If you're going 60 MPH=5,280 ft/min a "cold air intake" only needs to have a 0.1 ft^2 (3.8"x3.8") opening in order to supply an AF with a 528 CFM flow of "outside RAM ambient air" which no matter how you want to cut it is much cooler than the ambient air that's forced to flow through the A/C condenser, the IC, and the radiator!

In addition to being much cooler the "outside RAM ambient air" due to its RAM air effect also supplies the "cold air box" with "pressurized" air which reduces the restriction of the "cold air element" by 2" H2O.

This means there's two different ways by which a "cold air intake" reduces the workload on your turbo relative to the workload that's required for an "open element" AF... 1) the cooler air increases the air density at the compressor wheel and 2) the higher pressure air increases the air density at the compressor wheel.

Since MAF={(AD)(CFM)} lb/min an increased AD=Air Density lb/ft^3 means that it takes less CFM to provide a given MAF to the engine and less CFM means the compressor wheel rpm is lower for the same MAF. Conversely an increased AD means that more MAF can be provided at a given CFM.

 

Cool, another member capable of independent thought.

But you got to be careful, that's the same kind of attitude that earned me the title of "6637 basher".

 

I have said many times it's not for everyone. Some don't like the noise, some feel they MUST have a CAI. So be it. However, all this "you're losing power", "sky is falling" stuff you guys keep posting isn't necessary either. The 6637 has been PROVEN on the dyno and with OAs. That is undisputed.

Y'all enjoy another fruitless thread...