heating issues when idling 340 73 duster

LMFAO. According to that chart a 15# system would boil at around 195° c or 383° f. I don't think so Tim!

It's in Pascals buddy, it's not a chart for radiator PSI.

The point is, it's not a linear curve so 3° per psi is just a very basic estimate. My numbers are accurate.

And you do need to take elevation into account. It makes a bit of difference. I am at 880' above sea level. Water boils at about 204°

Not in a pressurized system it doesn't. Boiling water in a pot, yeah sure. Not inside a radiator.