Well, if it does not pressurise the cooling system right off, odds are its ok, at least the seal from the combustion chamber to the cooling system is. If the car is not mixing oil in the coolant (or viceversa) try replacing the thermostat and double check the accuracy of the guage/sender. Aux fan function has several players, the switch in the head, the a/c switch, relays, resistor and of course the fans and wiring. Check the fuses, they are either in the box or in the relays in the back of the box. (simple test, turn on the key and jump the a/c switch, if you get a/c clutch, jump the other switch) I've not seen a 606 with a cracked head as of yet and 103C is not really that hot. I'm inclined not to be too concerned until I see 115C myself. (my old 617 runs normally in the 100 zone at 75 mph, been that way for 200K, the old 103 in the wagon runs in the 105 zone in traffic)
The 603's I've seen with cracked heads (all of 3) were losing coolant with no explanation, just simply eating it. No excessive pressure, no trails and they would pass a pressure test with flying colors, however and a gas analyzer would get hits in the 5000 PPM range off the cooling system with pure water in 'em. There is also a simple, inexpensive tester that uses a chemical that changes color in the presence of HC/CO in the cooling system.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.