92 Ciera Coolant Flush

3.3L V6
144,660 miles

Winters coming along and since there's probably a little more water than coolant, I'd like to drain it all out and replace it. Do i need to open bleeder valves or can i keep the cap off until the thermostat opens and add as needed?

Also, I'd really rather not knock out the core plugs to get the coolant out of the engine, Would it be possible to disconnect the upper radiator hose and allow the engine to run, turning the water pump, thus draining it?

Im open to any other methods anyone knows about..

Ironically when i went to start up my car this morning, the passenger side had a puddle of antifreeze on it. heater core?

When I drain my coolant, I drain the whole coolant out by opening the drain plug on the lower part of the radiator. I filled with water and let it run for 10 minutes and drain the water. Put more water again and this time put the coolant flush solution bottle (1 quart) and run the engine for 10 minutes and drain it again but I measure the water that comes out so I can deduct on how much water I have left in the engine block that did not drain. I check my vehicle specs to see how many quarts/gallon of coolant it needs. I mix my coolant keeping in mind the water that is already inside the engine.