ISSUE: Cooling System. Losing fluid regularly; Re-filling resevoir at least twice a week when fluid is down to just covering the bottom of the resevoir.
Ford dealer changed the theromostat housing because there was visible leakage (more than the amount mentioned in the issue above). Continued to lose coolant, so Ford dealer pressure checked the Cooling System to include inspecting hoses and found no leaks.
Your feedback to what the problem is will be greatly appreciated.
When you can't see evidence of an external leak, the first suspect is a leaking head gasket. To verify that, or an external leak that is so slow the leaked coolant evaporates before it drips onto the ground, add a small bottle of dark purple dye to the coolant, then drive the vehicle for a day or two. Search with a black light including at the tail pipe. The dye will show up as a bright yellow stain that you follow back to the source of the leak.