A steadily increasing stream of coolant was being emitted from the bottom of the thermostat housing. Bolts should not have been too tight, housing was checked for warpage against a straight edge and found to have none. The thermostat was turned in a clockwise position and locked into the housing. There was a little copper-colored peg in the surrounding edge of the unit, is this the weephole perhaps? The cooling system's vent cap was open, and the car had not been run.
I was originally questioning the gasket in another thread because it had an odd fit, but others seem to think it was correct. All the material lined up with the holes & edges, simply a tab of gasket material was protruding from the top of the housing. This is also a new Motorcraft gasket from the same source as the thermostat.
I noticed a very small (1/8"?) 3 sided indentation at the bottom edge of the intake, where the housing meets. It looks as if it was designed to be there.
The previous aftermarket non-locking thermostat did not leak significantly, though it lost slight coolant over time. It was replaced for this reason and for its lack of a weephole.
I have thus far been unable to find the part number for this Motorcraft thermostat, XF1E-8575-BA, listed anywhere. I wonder what car it was designed for?
Thanks..