Taking the plunge. My journey as an O/O.

Not a bad idea, and worth trying. Radiator caps are cheap, but I had the cap replaced twice less than a year ago.

As for the pressure thing, the variable pressure is outside the radiator, the pressure inside the radiator is going to be pretty much the same at high temperatures, regardless of the external pressure because the radiator is a closed system until it reaches a set pressure differential and the thermostat (or whatever is in modern trucks) pops open.

The pressure differential between the inside and the outside of the radiator is what causes the relief valve to spill vapor (or even liquid in some cases.) At least pressure differential is the only way I can think of to have a mechanical system dump pressure from a closed system.

 

Is this something that would conceivably leak significantly at higher elevations, but leak very little at low elevations?

EDIT: I will have it checked out, regardless, if it's cheap maintenance. O-rings on a 700k mile engine are certainly a potential issue.

 

Another good idea if I can find a UV light and dye that I can leave in the coolant. Rather not replace coolant four times in only a little over a year. Three is enough. (Twice during engine rebuild issues, once a couple months back when the coolant tested weak.)

 

System has been pressure tested. No leaks. Exhaust was tested during dyno. No coolant in exhaust. Coolant reservoir is less than a year old, and no cracks. I can look into the EGR cooler line, but I think that was replaced when the EGR cooler was replaced during the engine rebuild.