in the end it dont matter which one to tap into, it still flushes through the whole engine.
or take both hoses off and fire it up, only one will push coolant out of it.
best way to flush it to me is to remove the t stat, and then put the housing back on, leave the hose on the housing, take it off the upper rad. yank the lower hose to drain the engine and rad, then put it back on, then put a hose in the rad, fill it, then fire up the car, run it till clear water comes out of the upper hose. then take the hose out of the rad, run the car till no water comes out the upper hose, then shut the car, put the t stat back in and fill with one gallon of straight antifreeze, NOT the 50/50 stuff. and then top off with water, bleed the air. done.
your cost, 15 bucks for new coolant. you 04 up guys dont even need a new gasket for the t stat most of the time.
