So I have a 2005 F150 Fx4 and I have had a problem with my truck overheating. The needle will move to the middle of the temp guage just like it suppossed to, but then after a while of driving 45 - 50 it will trip the guage and i get 3 beeps and the info center says to check the guages. I took it to my mechanic and he said it was the fan clutch or bearing and was a rather common problem. He installed a new one and sent me on my way. The truck ran fine for over a week, but last night i was driving home at night and we have recently had a huge drop in temp, so it was in the upper 40's or low 50's and my truck said that it was overheating. I cannot figure out what is wrong, anybody got any ideas. Also it seems to run on the highway fine but in the city 45-50 at 1100 rpms it always seems to overheat. thanks in advance

 

I was doing some reading and i would like to clear up a few things. When I said the truck overheated, i meant that i got the 3 beeps and the check guages, I have never gotten any steam or anything coming from under the hood. Also, it seems to either cool off or pause it i put the pedal to the floor, but if i drive it at granny speed it then tells me its overheating. Also, I live in florida, and its normally in the 80's so the drop into the 40's is pretty substantial. Thanks in advance.

 

well i have since the problem started replaced the fan clutch and the problem ceased for a few days but started again. Then I replaced the thermostat today and the problem has appeared to cease altogether. I think the thermostat may be the problem, but i tested it in boiling water and it appeared to function correctly. The ring around the thermostat expanded about 1/4" to 1/2". I think this may explain the overheating at 45-55mph. My hypothesis is as follows:
The expanding ring allowed a significant amount of coolant to circulate the engine at speeds below 45mph due to the decreased amount of work for the engine at these speeds. But at higher speeds and a more constant pace, the thermostat could not supply the engine with enough coolant to keep the temperature from rising above 240 degrees and thus tripped the guage to sending out an alarm. When the truck was driven above 55 mph on the highway, the speed barrier was broken and the air was then forced into the radiator and assisted the cooling system enough to keep the engine below 240F and thus the engine did not appear to overheat. Please let me know what you guys think. Thanks in advance