New to this stuff, Found this GM Forum with the hopes of someone answering the perplexing problem of how to get all the old coolant out of the 3800. In the old days you open a drain plug and presto..... Tried clamping the upper rad hose, block the overflow tube, blowing air in the bleed screw. I have only managed to get 2 gallons out and I believe it is supposed to hold 3 gallons. I have searched the web and to no avail. Do I just keep adding distilled water, run, cool down, drain, add more water, run, cool down till it gets diluted and then just add full strength, till I get to the 50/50. I just bought this 02 Monte SS from a friend who always had it serviced at the Dealer. Alas it had never had a coolant change, only has 60,000 miles but it is 10 yrs old and was never winter driven. WHAT'* THE TRICK

According to Alldata, the cooling capacity is 13 quarts. So it looks like you got it all out.

you are never going to get it all out, theres the block, heater core hoses etc. i use this run it till clear then add a gal of strait, then top off what ever needs with 50% mix

Just fill it, run it, drain it a few times.

"Just fill it, run it, drain it a few times."

That method has always worked great for me. The one thing I like to do is flush the heator core directly via a hose. I have flushed the heater core with a car wash high pressure hose (not full strength) when I did not have a hose available.

Buy a Prestone flush kit for around $3. It is just a tee you install into the heater intake hose that has a connection for your garden hose on it. Hook up the garden hose, remove your rad cap, and turn the hose on full. Run the engine a few times with the hose running until nothing but clear water is coming out the rad cap opening for a while. Remove the hose, cap the tee, and drain as much of the water out of the cooling system as you can. Close all the drain points, and add concentrate coolant in the amount of 50% of your total coolant system capacity. Top up with water. 50% of your cooling capacity will be filled with concentrate coolant, and 50% will be filled with water. This provides the proper mix.