239 Flathead Flush
 

Garden hose attached to the upper radiator engine mount. Will want to capture the first few gallons as it will be contaminated with antifreeze but after that it should be water/sludge. Alternatively, if you don't like the sounds of running water, you could fill it and drain it a couple of times to move the sludge out.

The engines in all these old Fords are sloped to the rear, and the flat V8's don't have any drain ***** at the back of the block. So draining the coolant doesn't really drain the whole block.

If you can park the truck facing downhill safely (wheels chocked, in gear, e-brake on), it really helps to flush from each thermostat hole on the heads, with the lower radiator hoses off. That said, the sludge that builds up in the lower back of the block is famous for being hard to get out without having the heads off, but it's the best you can do.

Be creative make a adaptor for the bottom hose for your garden hose maybe plastic with a tapped hole for shop
air. Run the water and short burst of air this is reverse flushing : watch out for years of junk comming out of the
head outlet. Same with radiator bottom hose and blast it. My bought new by my father 50 F6 now steaming and blowing its load caused from years and yrs of stop leak and whatever -block was half full of that junk. The
thought was stop leak for another days work. The engine back when, was Cody Ford Summerville Ma short block. still runs perfectly...

BEFORE I changed my radiator, I flushed with straight phosphoric acid. Then pulled pumps, had engine on down hill slope and blasted with pressure washer. Also took out T stats and blew into heads. Looks like new inside and no overheating here in AZ. I posted all this up. Id do a link if I ever remember how.