Drain Down & Rinse 2GM20F
The latest time I did this was last fall; to drain, I opened each petcock (which had about a 12" x 3/16" clear plastic drain tube attached) with the fill cap open. I refilled and rinsed several times, and each time filled the overflow tank then before starting the engine, I loosened the hose clamp on the right side of the fresh water pump (as you face it) and let the air out until water flowed, then tightened up the hose clamp (If I remember correctly,the thermostat is slightly above and behind that hose). This burps the air out of the system after water has filed the cyliner block. I disconnected and blew air thru the upper heater hose from the engine side to clear out all rinse water. After re-filling the antifreeze, I opened that hose and poured antifreeze in from the top with a funnel to insure that hose was full down and thru the water heater and then re-connected it. Again, loosen the hose clamp to let out any air at the fresh water pump. You may have some air still in the system that will work itself out after running, so be sure to re-fill from the filler cap and the overflow tank again after the system has cooled down.
