You're actually better off revving the crap out of it if it tries to overheat. Reason being that you're spinning the water pump and the clutch fan much faster.
When my 535i tried to overheat on the last BMW club run it was worst under load (up hills) at low revs. I just made sure to keep the revs sky high for the rest of the trip and it behaved itself.
And a clutch fan will mostly only affect your cooling at low speeds. If you were on the run I highly doubt it's the fan. The auxillary fan won't be the be-all-and-end-all of this either so I wouldn't look at that.
How long since you've done a full system overhaul? Possibly slightly busted water pump or malfunctioning thermostat?
I don't believe that a hot day and any sort of load should have any sort of effect on a car with a functioning coolants system. If any of those things affect the ability of the car to keep the temperature constant, it's because something isn't functioning.
You're not having much luck with this car are you.
Last edited by trive2; 12-16-2012 at 10:03 PM.