I have a 1999 F150.. 4.6L .. It's lifted, on 38.5's.. Has been for a while and has 150k miles on it... I'm having problems with it overheating.. It's not anything to do with the head.. (no head gasket or cracked head).. as I am getting no water in the oil.. Yet, it runs rough and overheats. Replaced thermostat and have had radiator flushed.. which seemed to work for a little while.. If anyone has any ideas.. PLEASE HELP!!

 

Fan spinning?

 

Yeah, everything seems to be working right.. The water just keeps boiling out. Could it be a sensor or something that has gone bad??.. I can touch the motor and it's not hot or anything like that.. I am out of all ideas

 

A radiator that has it's lower 1/4 or 1/3 blocked, reduces the total cooling area.
This is because the radiator is the horizontal cross flow type. The ends still flow between the top and bottom but not accross the cooling fin areas as it should.
Flushing is not always the answer in it'self.
I have seen this happen several times and it fools you.
How this often acts is the engine will stay cool while driving but as soon as you slow or pull a hill and stop the engine, the coolant pushes by the cap from the high pressure the heat causes.

 

Had a neighbor fight with an old car and overheating. He flushed the radiator, then acid flushed the radiator and replaced all hoses, then rodded the radiator, and then bought a new radiator and nothing worked. The car was still overheating. He finally had some kind of industrial acid flush done on the block (in the car) and it solved all problems (!). Turns out he had a bunch of scale in the heads that was preventing the coolant from pulling the heat off the engine.

Also, have you tried another new thermostat? I have had those bad out of the box. Is it installed in the right direction? Face it the wrong way and they don't open.

Good Luck