My son has a 2002 Protege5 wagon with the 2.0 DOHC, auto trans and 150k. 2 weeks ago he managed to gently get it on its roof. It was upside down a little over an hour before we got it towed to the house. It sat there for another 24 hours upright before I started it up. I did nothing to prep the car for that. it started right up and ran fine other than a ton of smoke - after a minute or so of running it sputtered hard and died. I immediately started it back up and an extremely loud knock started. I had it towed to the shop where it was diagnosed as having a knocking rod. Since the engine was junk I drove it home (about 3 miles) and after about 2 miles the knock completely stopped. I've never heard of this happening and am at a complete loss as to what happened. I called the mechanic and he was stumped but insisted that it was definitely a knocking rod. Any ideas?