I didn't see any plugs in the water pump ... but I didn't look for any either. DANG, I hope that's not it.

The Mitsu parts guy indicated that it has a problem with trapping an air pocket behind the thermostat which keeps it from opening (which is why the fans don't kick on either).

I tested the 1st replacement thermostat last night & it worked fine. I was going to drill a small hole in it to allow any trapped air behind it to bleed past. But there's already a hole in it with a brass plug. I pulled out the plug & will try installing it tonight & burp the system again.

FINGERS CROSSED EVERYONE (this is getting irritating - too simple of a job to be causing all this trouble)!!!!