Coolant change today. Rainbow - red

First coolant swap dome today. Old stuff was looking a bit muddy and not sure what color it was. Could have been green and orange mixed, not sure. So I drained, flushed, and installed BD chemical flush and went for a 50mi drive. Then flushed that out with tap water and then filled with beck Arnley red OAT coolant, and distilled water. System took 1 gal coolant, 1gal water, and a pint of water wetter fit in too so, perfect!
I feel like my 456 makes a lot of heat, it heats up just idle rather quickly, and it seems to develop a lot of vapor pressure too. How does the car maintain proper vapor pressure anyway? The overflow bottle cap doesn’t seem like it is a precision pressure blow off. Is it? I also cracked the stat air bleed, but I didn’t take the stat out and test it, which I already sort of regret.

 

I did, as I usually do with any vehicle, but my owners manual says full cold AC which I thought was odd. My ac don’t work so I forwent that lol. I never really understood why full heat matters, I think it only matters to force mixing valve to open hot line but maybe they say use fan to ensure it really moves? I dunno. But it mades plenty of hot air and water. I did wish they had informed me that you dont need to remove the from belly ban to get to the drain valve but oh well.
Also, ended up driving over a full gallon of coolant and exploded it, oops. Oh well still saved a bunch of $ over having a shop do it lol.