I've got a problem that no one seems to be able to figure out. I've got an '02 Opti that is giving me overheat faults. The impeller was recently replaced and the water pressure reads ok on the diagnostics. Thermostats have been replaced. My mechanic cleaned some trash out of some areas (grass and such). The catch is that it's happening at or near an idle and it's jumping back and forth between cylinder banks. One time it's port, the next it's starboard. Take the prop out of gear, run the engine up and reduce back to idle, the alarm goes away and doesn't come back until the next time I shut down and restart. Repeat the same procedure. I don't think it's really overheating because it's happening so fast, and then, amazingly, it cools just as quickly? Not likely. Has anyone seen this before? Any tips would be appreciated. I'm about ready to dump this thing in the bay. It's been an ongoing issue now for months. Help!
2002 Mercury Optimax 
