I have a 97 Cavalier with 180k miles, just recently its been overheating. When it starts to overheat it makes a nosie sorta like its boiling in my res. tank. after the noise coolant forces its way out of the cap and I lose all my coolant. The thermostat has been taken out by whoever i bought the car from. I ran some scan tool tests at school but it doesnt seem to gave me much. If anyone can help thatd be great, thanks. Id also like to add that my teacher told me he is 90% sure its a bad head gasket. I have a feeling its not because I checked my spark plugs, there fine, i havent noticed any white smoke and i do get heat inside the car when it has coolant. Im supposed to start working on the head gasket at school within the next couple days but i dont want to go through all of that without being 100% sure.