RLDSL, i would like to know more and how you set up a zero pressure system, I see you tow with your rig and you have no overheating issues? I know when I am pulling a big hill WOT in 4th the engine temp will climb to 220 and stays there that is when I drop a gear to 3rd over and it will cool down some.
As mentioned, I'm running
Evans waterless coolant . You run it straight with no water and no SCAs needed and it doesnt require frequent changes as there is no water in there . The stuff will cause you to run a tad warmer, but with a 375 deg f non pressurized boiling point, it's almost laughable.. With no boiling you get no localized hot spots, = no warping or cracking or gasket blowing, in otherwords, if it gets hot, it gets hot, and you let it cool back down, but none of the usual associated bank account drainage and long shop time
THis stuff has saved a few of my engines ( and a few family vacations ) Stant used to make good zero pressure caps but the only ones they have now look like they were made for chinese tractors, so you have to take a fixed pressure cap and snip the suction seal stem off to make a zero pressure cap now although it is a bit more restrictive than I like, I think I'm going to make a fitting into my upper hose attachment that goes to a surge tank to make up for that