mguy

Need your help to solve this mystery:-\ Vehicle: 2001 Forester S with 104k miles Diagnosis from Smart Service, Seattle, WA during buyer's inspection: medium oil leak from Left Head Gasket (HG) & minor leak from Right HG (even though seller had replaced full HG Set <1 yr ago). By "medium" leak, the mechanic explained that if the car was left idling in one spot for a few minutes, there would be drips from the Left HG. Seller: Injected florescent dye into both coolant and engine oil over this weekend and drove over 200 miles. When he took it back to his HG mechanic today (still within 1 yr warranty period), there was absolutely no leak (no florescence). Assuming that neither mechanics are wrong, is there a rational reason why there would there be a significant leak found last Friday but no leak found after driving 200 miles this weekend? How do I resolve this mystery quickly and decide whether or not to buy the car? I trust both the seller and the mechanic. At this point, the seller is really pissed off at the inspecting mechanic and just want me to decide to buy the car or not by tomorrow AM. Your expertise appreciated!

Follow-up question: After replacing the EJ25 with a new head gasket set, how long do you expect it to last? Will the head gasket blow again in approx 100k mile due to the design of the engine? Or will other parts of the engine fail before the new head gasket fails again?

I want to applaud sonyhome's efforts and summary. As a newbie with no engineering training but interested in buying a over 100k mile subura, I had many of the same newbie questions which were not answered after browsing this site for over 5 hours.