When I was pulling my trailer up a steep grade on I-8 towards San Diego this November, I noticed all the radiator water on the side of the road every mile or so. My coolant temperature was hotter than normal, the dash gauge was above 190. My Edge showed it maxed at 204. What is too hot for this engine? Is 204 just fine, or is that getting close to the limit?

 

I doubt that I'd worry about a 14 degree rise in temp.

Water at standard atmospheric pressure (14.69lb/in) (i.e. sea level, standard day) boils at 212F. For every pound of pressure, it raises the boiling point about 2 degrees F (actually a bit more).
Let's say that you have an 18lb cap on your rad. You can say that the boiling point of the coolant should now be 248F.

Very simply calculations, but it gives you an idea.

 

And running around 190 isn't going to hurt it either. Most fellas will upgrade to a 190 Thermostat anyways. I doubt you hurt anything by running close to 210 lets say either.

 

Check the radiator to make sure it is not clogged. The puke bottle will allow a little mist and oil to get into the fins and block the air flow.

 

Many vehicles can operate at 230 degrees and perhaps slightly more without incurring damage. Good oil (SYN), properly fitted components (pistons), and cooling system in good shape have a direct bearing on surviving.
As someone else indicated, check radiator for external blockage. JMHO
Most of the "heat" comes from unlocked torque converter during hill pull. Go to OD lockout when encountering heavy pull. Downshift early into second and even low gear. Keep RPM's up as converter more efficent at 2500-3000 RPM.

 

Thanks, guys. I've checked the radiator and things are pretty clean. Squirted it off with a low pressure hose, there just wasn't that much dirt to rinse off it. And, yeah, dozer, I have noticed that if I run with the torque converter unlocked pulling up a hill, I do generate more heat. Most times I run with the TC locked up, only unlocking if I can't hold the engine revs. In that case, I unlock, get the revs and speed up, then lock it again.