[Taylor95]

So my wife's 2001 Subaru Outback 2.5 H4 has been overheating lately. The onset of the problem was on a recent trip. I got a P0420 (I think this is unrelated) and the car started overheating about two hours later. I since cleared the code and it hasn't come back. After the trip I discovered that the overflow tank had a lot of fluid over the full line. I replaced the thermostat, radiator, and radiator cap but the problem persists. The coolant was milky, which is indicative of a head gasket problem, although the current head gasket is only about 20k miles old. Any suggestions on next steps with this car? Will fixing the head gasket stop the overheating, or is the head gasket leaky because of getting too hot?