If I use a higher pressure radiator cap, will my engine run cooler?

 

No it will not run cooler. 1 lbs of pressure will raise the Boiling Point of your coolant by 3 degrees. So if water boils at 212 Degrees and you add 1 lbs of pressure, it will boil at 215 Degrees. If 10 lbs, it will boil at 242 degrees. Best Basic mixture of your coolant should be 50/50 water and antifreeze, which, IF I Recall, is a value of -34 degrees of freeze protection. Anti-freeze alone is not recommended and you should use the recommended pressure cap for your vehicle. Years ago engine thermostats where 160 degrees and pressure caps were 4 to 7 lbs, today's engines use typically 195 degree T-stat's and pressure caps of 15 to 22 lbs.

One of the best things you could add to an older vehicle is a coolant recovery tank and a recovery type pressure cap of the correct lbs pressure, as all later vehicles have.
Cap

 

Thanks for the help

Thanks for the help

 

Thanks for the help