okay here it is... i have a 99 f150 with a 5.4 motor.... well... since its getting hotter around here, i thought that i would start running the a/c... well i did... then found out that my fan clutch was out... (very quickly found out that i might add)... so... i changed the fan clutch.. now it works like its supposed to when the a/c is off... i blew the radiator out when i changed the fan clutch... now when i turn on the a/c, the once the engine is warm enough for the fan clutch to be on, it stays on all the time.. (killing my fuel mileage) so...m what should i do? a different fan clutch? flush the coolant? put in a low temp thermostat? ??? another thing is that with my job this summer my truck will be doing a lot of idling (its a must) i dont want the fan clutch on all the time do i? i dont know what to do..... can someone give me some suggestions on what to do or has anyone ever had this problem???
-marshall
-99 f150 5.4 xlt 200,000 and still tickin

 

the fan stays on untill the water temp drops back to normal range. look at the temp gauge, what does it say? your right, water pump poor, thermostast stuck, low water level, or fan clutch temp off. hard to say which, need to narrow things down.