I have a 2004 WRX wagon (more or less stock) with 108k miles (which I love and is otherwise fairly good shape given it's age). When I was driving last week, I hit 5k RPM and suddenly the engine started making a clanking/knocking noise. I promptly brought it to a mechanic. To my untrained ear, it sounds like a bearing is being knocked around the engine. This noise only occurs starting at 2k RPM. If I keep it below that, the car seems fine (which means I can go as fast as 40 MPH ;-). The car starts without a problem, did not overheat, and has no check engine light. The mechanic says it a lower engine noise so he thinks its a connecting rod (bearing) that went bad. A friend of mine who used to build cars at GM tells me it's potentially driveable for many more miles which would be helped by using a thick oil like 20W50. So hear are my questions:
1-Does the noise that I describe (knocking noise starting at 2k RPM) sound more like a Turbo problem (I thought it was an upper engine noise, but I'm no mechanic) or is it more likely the mechanic is correct and it's a worn connecting rod?
2-I would think it would be easy to confirm if it is the turbo or the engine by temporarily disconnecting the turbo. How easy is it to disconnect the turbo long enough to diagnose whether it's the engine or the turbo & how long should it take a mechanic to confirm this (since the mechanic I showed it to swears this isn't the case)?
3-If it is a worn connecting rod, what are my options and how much would they cost? I would not be doing any of this work myself. The mechanic was unable to find any used or rebuilt WRX engines ANYWHERE in the US and said my only option was a new engine, which he quoted at $8800 installed. While I love my WRX, it sounds kind of crazy to invest that amount in a 6 yr old car with over 100k miles. I put on about 18k miles a year and would be willing to spend up to $3k-4k on the car if it would give me another 30k miles (such as an engine rebuild), so I can get another 1-2 years out of it, when my needs will probably change (need a larger car, etc). If you think it's a lost cause given these constraints and I should just get a new car, say so.
The WRX is currently located in Long Island, NY, if that makes a difference (or if anyone has a good referral). Thanks.