So, my wifes 03 civic lx is overheating. have had it for a year, and its done this stuff off and on for a while. over the summer it would overheat when the ac was on and the car was sitting still. as long as you were moving or the ac was off it was fine. i have not noticed any leaks except for the fact that it spews from the reservoir after running for a while. mainly on warmer days. i did a pressure test to the coolant system and it held 16psi (cap rating) perfectly. even let it warm up to see if maybe things were expanding and allowing things to change, but stayed fine. i had already replaced the radiator and fans, the fans didnt seem to be going at the right speed, both were a little slow, and since the radiator had to come out to get those, i changed it too, it was cheap enough. cap was changed then as well. when its cold and the heat is on, heat works great as long as you are driving. start coasting or come to a stop and it goes cold. any thoughts on what else to check, all i can think is head gasket. which i dont want. lol. but, i have no smoke or sweet smell in the exhaust. no oil in the water, no water in the oil. i can only think that there is a big enough hole to allow exhaust gasses into the coolant and causes it to push the coolant into the reservoir and blow out. havnt done a sniff test yet. school lets out after the 11th, then i can devote more time, which i mean i will have to.