Hello! I've been scratching my head on a 2007 pt cruiser that originally came to me because it intermittently overheated, I replaced the thermostat with a fail proof stat, and manually operated the fans on both speeds with my computer to check them, it worked good for several weeks but now my customer says it intermittently overheats, and runs ice cold some times, I'm leaning toward the ECT sensor but I'm not 100%, and ideas? Thanks in advance