I asked a similar question in one of my threads about a 235 with a 7 lb cap
Got this response from hotrod Lincoln
The 7 lb. cap will only add a few degrees before a boil-over happens. If the radiator and the heater core will stand the extra pressure without springing a leak, the 7# cap adds a bit more safety margin. The boiling point of water, or a 50/50 coolant mix rises 3 degrees F. for every pound of pressure on the system, so a 7# cap will add 21 degrees, to produce a boiling point of 233 degrees.
It's not uncommon for the coolant temp around the cylinders to rise above the boiling point after shutdown, causing the cap to "puke" a little coolant. Unless you have a recovery tank, that volume of coolant will be lost. With a recovery tank, the coolant will be drawn back into the radiator as the system cools down. It's not an original-equipment item, but it will certainly help the radiator stay full. I have used a 1-quart rectangular metal can like brake fluid or paint thinner comes in as a recovery tank, with a piece of copper tubing soldered into the cap that extends to within 1" or so of the bottom and a vent hole in the top. Just run the radiator overfow hose to the tubing and put a couple of inches of coolant into the can. The can is bracketed somewhere close to the level of the radiator cap, like maybe on the core support or one of the angle braces from the firewall to the core support. You'll need a radiator cap with a one-way valve in it to allow the coolant to be drawn back into the radiator on cool-down.
Jerry
I run a 180 thermostat and only overheated once stuck in a drive thru, I was low on coolant.
It will run up to 195 while driving up a grade.
