which one is the return hose back to the engine. I am going to do a radiator flush and figur If I disconnect the return hose then I could run the engine and the coolant from the radiator from the block would all come out. is this safe to do???

 

Upper hose flows from the engine to the top of the radiator.

Lower hose flows from the bottom of the radiator back to the thermostat housing on the engine.

But I don't think it's safe to do that. When there's no coolant in the head, it won't take long (seconds) before you turn it into a boat anchor.