My 96 f150 5.0 with 200,00 miles has been running hot, with the indicator 3/4 across the normal ban after a few miles but I have no boil over but I am using water. I have replaced the rad. cap, flushed it, replaced the tstat, but don't know why still hot. Even worse when towing boat. I think that maybe my catalytic converter is clogged or pump is not pumping. Oil is normal. Any ideas?

 

Did you ever think that your water pump may be starting to go out?

Did you do a reverse flush?

 

Might want to take a look at the fan clutch.

 

I ran it with the cap off and when I increased rpm I could see the water level drop indicating good flow.

 

Did it ever get back up to pressure where it started to come back out and starting spilling onto the ground?

 

I didn't let it run that long. When I let off the gas it just came back to the top of the cap area, maybe a little spilled out. What should I look for?

 

Have the radiator flow tested.
Bet the lower part is plugged, reducing the cooling capacity.