my beloved outback has been running warm and coolant bubbling out the overflow tank when slow speed driving. head gaskets are only about 20k miles old so was really hoping to avoid that process again. decided to start throwing every other possible part at it first.

this is the bottom of the rad, but its the side facing the engine and not exposed to road gravel and other debris. current working theory is mag chloride road salt and filth accumulated in the bottom and oxidized the fins and channels.