1998 Subaru Outback Overheating-

I had overheating problem on the highway-towed car to Automotive Clinic in San Francisco. They said I needed new radiator and hoses, so I installed for over $800. Couple weeks later, overheats again, this time said I need new head gasget, so I go ahead and replace all–$2200. I drive to Chicago and back to San Francisco in couple months, soon as I get back, my car overheats AGAIN. Now back in the shop, and they told me the head gasget blew again…they have taken all apart, and now say they can’t find out whats wrong. The coolant is leaking, but they don’t know why…it failed hydrocarbon testing. What can it be? What can I be reasonably responsible for, or what do I do if they want me to pay for more work after I’ve just spent $3,000 with them?

Clarify please:

You say they told you the head gasket blew again, but then you say they have it apart and don’t know what’s wrong.

These two statements don’t add up.

Is the mechanic who’s working on this car familiar with Subarus? Is the coolant leaking externally or is it leaking into the cylinders?

In addition to the clarification that mcparadise asked for, I would like to know if the mechanic originally replaced both head gaskets, or if he replaced only one of them.

If he replaced only one (which shows that he is not really competent), then it is entirely possible that the other head gasket is now in need of replacement. On an engine of this type, head gaskets are always replaced in pairs–if the mechanic knows what he is doing.

If the mechanic did replace both head gaskets the first time that he worked on the car, then the only two possibilities that I can come up with are–

He failed to check the cylinder heads for warping. When an aluminum engine overheats, cylinder heads need to be checked for warping and planed or replaced as necessary. Failure to take this step indicates a less-than-competent mechanic.
and/or
He did not properly torque the head bolts when reinstalling the heads.

Truthfully, none of these scenarios–coupled with “they can’t find out what’s wrong”–make your mechanic sound like someone to whom I would entrust my car.