Coolant capacity for a 68 C20 396

[northerngmc]

I purchased a 1968 C20 with a 396 this past spring. I am getting ready for winter ( it snowed about 20 miles west of town yesterday!) and tested the antifreeze strength in the old girl. It tested -25 C or about -10 F, which isn't cold enough. So I need to drain some out to get the strength up to -40 or colder.

So while I am at it I might as well drain it all, flush it out with water and refill with new antifreeze and a new thermostat.

So any idea what the capacity is of the complete cooling system (rad, hoses, heater and engine)? The truck is a 1968 C20 with a 396 and Turbo 400 with a trans cooler.

I have done some searching and seen anywhere from 2 to 4 gallons. Anybody know for sure?

I want to know the capacity so I can add antifreeze after the flush without over diluting it from the water left in the system.

Also are there drains in the block of a 396? I was searching and someone mentioned draining the block using the drains when doing a coolant flush.