I just flushed the system with Peak radiator flush and added new Prestone Premixed Dex-Cool antifreeze. It took about 1.25 gallons of premixed antifreeze. I plan to flush the system every 5 or 6 years and replace the antifreeze every 2 to 3. Steps were as follows: I removed the thermostat. It's your choice on whether to do that. With…