Ford: Running Hot and melting Throttle cables, degree thermostat, radiator cap

Question
I have an 85 ford F150, 4.9 liter Straight Six; I recently had an engine from an 87 ford F150, 4.9 liter, straight six. There didn't seem to be any differences when installed. I just put about 20,000 to 30,000 miles on the engine since the rebuilt. The engine would run High in the heat, sometimes I would start it up and it would run right in the middle of the Normal range. The last few days it’s been running right on the far right line of the normal but hot. It’s been melting Throttle cables. My brother was telling me it might be the wrong water pump, He thinks it’s because it might be for a serpentine belt. I don't know if it is that or maybe it’s a bad thermostat. Possibly even a plugged radiator. Any information you can give me would be much appreciated. Thank you

Answer
Josh, there are a lot of things that can make a truck run hot.  I would start by replacing the thermostat.  (make sure it is a 190 degree thermostat)  Next, I would probably replace the water pump.  After these two things, all you should have invested in the problem is about 40 dollars.  Let me go back a second, when the engine it hot, check and make sure the fan clutch isn't locked up.  You can do this by turning the engine off and trying to turn the fan.  It should spin will very little resistance.  If it doesn't, then it has locked up on you and can cause your engine to run hot.  Also, your if your timing is off, the truck will run hot.  Is the truck starting after the first turn of the starter?  Does it try to "diesel" on you when you turn it off?  So far you have a thermostat, water pump, and fan clutch invested.  About the only thing left to do is replace the radiator or take it to a shop and have it professionally flushed.  A flush job in Arkansas costs about 60 dollars.  I almost forgot about the radiator cap.  The radiator cap can cause pressure to be released early allowing the thermostat to open too soon, and eventually, your truck will run hot because the radiator hasn't had time to cool the water in it.  That is about all I can think of, besides a cracked head, leaking water, the obvious stuff.  I hope this helps,   Jason