3sfe stick, ac removed 221k sometimes after i stop driving i notice that the top hose is bubbling inside and the overflow tank is bubbling up, not enough to overflow, driving everything is fine though even pushing it, havent lost a drop of coolant and no mixing in oil
Agree probably a head gasket... That was the first sign my 3sge had about a year ago... I waited a bit but it kept getting worse so finally I did the gasket and found and repaired a few issues with the head. In addition to the bubbling, I also would hear a slight sloshing noise through the heater system, which I assume was air getting in. Vicdat
You can make a leak down tester out of a compression tester and then find out the whether or not its the head gasket
