I have a 2014 F150 FTX 5.0L and every time I run it on the highway or freeway the cooling fans run on high when I slow it back down in the city. but if I just run it around town the cooling fan never goes to high speed. What could be the issue?

 

Its likely because you have the AC on.

 

Check your coolant levels. You may be in need of a new thermostat. Use Motorcraft only.

 

After reading many posts on this subject I went ahead and purchased a new Motorcraft thermostat and during the installation I noticed that whoever owned the truck before me not only put an aftermarket thermostat in but they had the wrong antifreeze in also. So, while I was at it, I flushed the system and put in Motorcraft Yellow antifreeze. Now even though the temp gauge is reading about the same as before, the fan never goes on high. I don't get how an aftermarket thermostat could cause this to happen, but it did. I'm just glad the issue has been resolved. When I was installing the new thermostat, I noticed it had an aftermarket oil filter and I have read that we need to use a Motorcraft filter. What kind of issues could this cause by running an aftermarket filter?

 

the aftermarket thermostats aren't the correct design - theres a diagram floating around that shows how the thermostats work in these trucks and its not the same as old school ones.

aftermarket filter wont cause any issues. Motorcraft is usually considered a high quality filter but there are other quality aftermarket ones. If it's a cheap one it may not filter as well

 

That makes sense. Must be something to do with water flow rate or something like that.