Since my 3.8 engine hasn't had a change of coolant in over two years when the odometer turned 100,000 recently, I decided to do a thorough job of it. I used the shuttlecock on the radiator and drained as much coolant as I could. That constituted about 6 quarts. Then I filled the radiator to it's limit with water and a few table spoons of Baking Soda (an old farmer told me that helps clean the system and I have done that on most of my cars). The recommended procedure would be running the car and heater with the plain water mix for a few days, drain it and then fill with 50/50. However, I have decided to try and flush the system thoroughly, so I ran it with the mixture for about 15 miles and then drained it. I was surprised at how thick it was with anti-freeze. Consequently I repeated the procedure of filling it with plain water and baking soda then driving it. Now, I am waiting for the engine to cool down before I drain the plain water out. I suspect that the waste water will still have anti-freeze in it. However, I am skeptical that if I add the glycol mix filling the radiator, I won't have a proper ratio given that the engine must hold more than 6 quarts or the radiator fill. I saw in a manual that the capacity is roughly 11 quarts. Should I add pure anti-freeze instead of a mix? I am also planning on using a Flush as directed on it's container. That says drain the anti-freeze then add the Flush and fill with water. After that you run the engine with heater for 20 minutes. Then they say drain the radiator, fill it with plain water, run it for another 20 minutes and then drain. I followed this procedure with another vehicle but wonder if I have the right ratio of glycol in that engine given that I added 50/50.