I too would like to use the current C or E class fan, but the fan motor is too THICK between the pullys and the radiator.
I found a SPAAL (sp?) fan that's 16-inch in diameter that pulls 2500 CFM at 25A 12VDC, but it will have to be off-center. Any problems with off center?
Yes, I've seen the probes that goes into the radiator fins, but IMHO they are hokey.
Any other ideas?
Someone mentioned just running the aux.fans at say 90-C?