Best coolant for our 60-70's Mopars?

the last time my engine overheated it was due to a leak, = low coolant , glad I was not paying $50 a gallon. all liquids boil at a certain temp, I do not need higher than 50/50 mix of fairly fresh standard coolant and water gives. I pop off 1 end of the lower hose around every 5 years + refill , for the last 30 years