I took the MH to Ford today and the temp shot up to 245F without any physical signs of overheating. A board member answered my thread in the FORD section. His name is AUTO and he really helped me with this TSB.
I'm going to post a thread in case it might be of help.
06-21-15 MIL ON - DTC P1285 / P1299 - 5.4L 3V / 6.8L 3V - FALSE OVERHEAT
Publication Date: October 13, 2006
FORD: 2005-2007 F-53 Motorhome Chassis, F-Super Duty
Some 2005-2007 F-Super Duty and F-53 Motorhome chassis vehicles equipped with a 5.4L or 6.8L 3-valve engine may exhibit an engine temperature gauge indicating an overheating condition with the malfunction indicator lamp (MIL) on with diagnostic trouble codes (DTCs) P1285 and P1299.
Performing normal engine cooling system diagnostics in Workshop Manual, Section 303-03, if it is determined that the engine is not physically overheating (coolant expulsion), install a new thermostat and crossover pipe. They have been revised for improved cooling system flow characteristics.
PART NUMBER PART NAME
7L3Z-8575-A Thermostat - 5.4L
7C3Z-8575-A Thermostat - 6.8L
3L3Z-8C368-A Crossover Pipe - 5.4L
3L3Z-8C368-B Crossover Pipe - 6.8L
Eligible Under Provisions Of New Vehicle Limited Warranty Coverage
Note: Normal would be from 190 to about 220. The actual boiling point of the system is about 262. 212 water+5 for coolant +15x3 for cap pressure =262.
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