I have a 2009 Saturn Sky 2.0L Redline. My car started to overheat at the end of February this year. I had replaced the thermostat that I replaced last year thinking it was it and aired out the system and thought it was fixed and overheated again but up to 234 degrees. The Heater blows cold and overheats, I was told it was a water pump so replaced that but I have not replaced the thermostat(it's not the oem one) at all and aired out the system after adding coolant. The car still overheats with heater blowing cold and when I drive the car it overflows the overflow tank. I had a friend do a compression test after and the compression is fine. When we running the car in the garage, he lifted the overflow tank and it was overfilling when I was doing about 1500 rpms and looks like coolant is getting into the overflow like it has a lot of airbubbles, the fan does come on at the right time. I don't know what it is and need help figuring it out. DDMWorks told to me to check the if the fan is blowing cold or hot to check between the belts and fan and it is blowing cold which he said that it should be that the thermostat isn't opening cause of all of the air in the system or could be a bad thermostat. I hope y'all can help me on this. Thank you!