Truck gets hot randomly

[Markmartin01]

So I have a 91 RCSB Z71 that likes to get hot but completely random when it does. Sometimes at idle, sometimes at 55, air on or air off, no certain situation seems to trigger it. New radiator, water pump, with or without thermostat, electric fan with shroud. Engine was rebuilt a couple thousand ago and was really clean inside but water does have rust tint after several flushes. Standard bore. Good fel pro intake gaskets with the rear ports blocked as I think is proper for the year, timing in spec any idea what I may have missed here?

 

[JWOK]

Have you verified it is getting hot and not just a false reading on the gauge? Have you noticed any running problems? Is the fan pulling air the correct direction and activating at a reasonable temperature?

 

[thinger2]

Assuming that all else is correct. Which might not be the case.
I would make sure it doesnt have air in the system or is sucking air into the system.
Like I say, that assumes a lot of things based on your post but it is easy to figure out and can cause those problems

 

[Eveready]

Betting on a defective thermostat opening and closing or maybe some rust/crud circulating through the system and intermittently clogging the thermostat.
Suggest flushing that pup and new thermostat ASAP.

 

[Markmartin01]

You know, it has blown the cap a time in the past but I'm not totally trusting the factory gauge. It showed to be above 260 once but wasn't bubbling so I'm not trusting the gauge. May put a mechanical gauge on it for ***** and giggles.