In the past several months ive had several issues with the cooling system. I will try to be as clear as possible to give you the big picture. These things are in chronological order 1) Had a thermostat fail. A fairly new one (maybe 2500 miles MAX). Bought a new one and installed it correctly per IAP video. 2)Heater core (or valve) started leaking in car. I bypassed it. I had formerly installed a Tee at the heater hose which I then noticed was leaking when car was hot. i removed it and ran straight hose still bypassing the heater core. 3) I burped the system by raising it in front and letting it run 30 mins with the cap off. I did see air bubbles at the rad. I drove it a while then topped it off. it ran at normal temps that day under a variety of driving conditions. It seemed obvious when the thermostat opened as the temp would dip back to the 1 (in 190). Never climbed to any temp that made me uncomfortable. 4)the NEXT day the car ran hot. Say 210 on the freeway. climbed to 225 sitting in traffic but I wasnt idle long enough to see it go higher. Back on freeway dipped to 210 again. Got home and parked it. 5) the next morning I noticed that my overflow bottle looked much FULLER than it had before, like maybe 3 inches more fluid in there. OK, my general sense is that the system is over pressurizing causing systematic leaks and failures but I dont want to jump to any conclusions. One question I have is regarding air in the system. What does that actually cause? Is it a blockage? Does it just wreak havoc with the temp sensor in the head? Other question is whether any of the above rings any bells, anything I should focus on? thanks!