This winter, I could not get any heat when driving to work in the morning. Coolant temp is usually under 140° for most of the drive. Each morning as I drove, I would blame myself for installing an Autozone "fail safe" thermostat instead of a Motorcraft piece.
Sufficiently motivated today, I bought a new thermostat and upon removing the old one discovered what is seen in the pictures. My SWAG is that is a piece of the inner spring from the lower radiator hose.
Tomorrow, I should have heat in the am!