I also have a 2006 fusion 900 and have never had an overheating issue. maybe something is wrong with the heat exchanger or the temp sensor? This is a common problem apparently for some people, so SLP makes a vent kit specifically for the 900 to help cool the engine and the clutch/belt. take a look into those and see what might help you. some refer to it as the "hot air elimination kit"
SLP Hot Air Elimination™ Kits help reduce stagnant underhood hot air to maintain higher horsepower by delivering additional cold air intake and hot air escape from the chassis. The kit for the left side helps to keep the clutches running cool, which considerably reduces the chance for performance loss due to heat saturation and improves belt life. The kit for the right side helps to reduce underhood heat given off by the exhaust system for a more consistent running engine. Vents utilize a powder snow pre-filter that repels snow and water, yet allows air to pass right through. These vents are sold in kits for the right or left side or as individual components by special request. Each kit contains one air inlet grate, one outlet grate, required fasteners and detailed instructions.
Kit Contents:
Left Side: Belly Pan Vent, Side Panel Vent, Pre-Filter Backing Shield and Installation Hardware
Right Side: Belly Pan Vent, Side Panel Vent, Pre-Filter Backing Shield and Installation Hardware
Note: Vents can be purchased individually, please inquire.
http://www.startinglineproducts.com/catalog.cfm?pageID=detail&catalogID=3&catID=16&productID=692