I have an FX35 with 128K well maintained miles, most at the dealer. About two months ago, car overheated; dealer changed the radiator.
Two weeks later, overheating occurred again; dealer then told me there was air in the system and all should be o.k.
Overheated again three weeks later, and dealer could not duplicate the problem.
Tomorrow going back to dealer since it almost overheated again yesterday.
As part of my investigation, I note that the coolant overflow tank gradually fills with coolant, without allowing coolant to return to radiator when car cools overnight. Eventually, the overheating occurs when the overflow tank fills; then coolant is expelled from overflow tank.
Overheating has occurred at various speeds; once when driving at steady 35 mph, once when driving at 50 mph, then again when decelerating from 65 down to 25 off a highway ramp. When overheating occurs, check engine line comes on and flow of fuel through gas pedal is barely possible (probably a computer safety device to prevent engine damage).
The day after the overheating occurs, FX runs fine until the next time.
Dealer has stated that they also have another FX with about 130K miles which overheats all the time, and they can not diagnose the problem.
Anyone have a suggestion as to what may be the cause? Dealer claims they already checked water pump, all pressures, etc. I found something on-line about the radiator cap gasket failing over time that might cause overheating, but they changed the radiator cap during the last visit.
Anyway back tomorrow for a loaner vehicle; this time I will instruct them to keep the vehicle until it is diagnosed and repaired, since the overheating occurs without warning.