My engine usually runs between 190-200 but the other day it was really hot and carrying a decent load up a hill on a highway, the temp got somewhere in the 215 F range, it looked like it was getting close to 220 and i am not exactly sure why - it was not that steep of a hill really. After a few more miles i had to get off the highway anyway and once i got to a stoplight it came down to normal temp and stayed there. But i was wondering, if this happens again, at what point would i want to pull over so as not to overheat? I believe my rig has an "idiot light" which signals overheating, which did not come on, although i can't say for sure if it even works.
Any advice on this one?
thanks!
Paul

Overheating is when the engine coolant starts to boil.

Plain water in an open container boils at 212F.

50/50 Water/Antifreeze mix in a 16psi coolant system and your boiling point goes to about 235F.
You don't want to get that hot or maintain temps above ~220F for very long.

6.2s had an optional 4 core HD radiator that works great if you don't have it already.

Paul make sure radiator and AC cores are clean, a retuned fan clutch will help, I get worried any time mine goes above or even starts to heading the 200F mark, coolant is supposed to keep it from boiling over but these engines are bad about overheat cyls 7 & 8 are poor flow to the back of the engine.

What year was the donor 6.5 NA engine, it is possible a 97+ pump and dual themostat could be added for more flow, one trick that works to pull away heat and you can't stop you know "next exit 50 miles" shut off AC roll down the windows, & turn on defrost to max hot it will pull some heat off the engine by blowing air across the heater core, miserable drive that way but can keep an on the edge system from boiling over.

If you don't find anything wrong with the cooling system, maybe the rad isn't sized properly as TDG suggests, remote bypass dual filter set up will help some as more oil to heat up almost 2 qt., and also a remote 12v fan cooled trans cooler will help as well as less trans heat would = less for the radiator to try and cool. I think all 6.5 Diesels NA or TD had a trans and an oil cooler did you bring those over in your swap?

A 50/50 coolant mix with a 15 lb. cap will take the boiling point to 265 degrees. I have my spare tire mounted on my front bumper so the engine temp will get to 220 degrees going up a steep grade in the summer. It does not boil and I have a 7 lb. cap. If the temp starts to go over 220 then I just downshift and that cures it. My engine did boil over in 2000 in Nova Scotia when the alternator belt broke and then it took out the power steering belt so I had no water pump. The temp was at 265 degrees when I noticed the problem. My engine wasn't damaged, but I sure don't like my engines to boil over!!!! The reason I run 7 lb. caps is to save my radiator, heater core, and all of my hoses.