I use the "crockpot method" at least 4 or 5 times a year. Make sure you set the temperature on LOW. If it is set on high, you will cook that engine and it will change color. I use Prestone antifreeze. Yellow container...undiluted. Not the premixed stuff you can buy in the stores. The antifreeze is green in color. I soak overnite on LOW temp. Never had a problem. Good luck