Another thing to check and quite common on the mondeo is the coolant pipe in the drivers wheel arch. There is a metal coolant pipe that runs right by the drivers wheel arch it comes from the front and runs around to the back of the block.

mine was like it for ages and the garage couldn't find it, the pipe tends to corrode and in mine was just a little pin prick hole, it never leaked much so you couldn't notice it on the floor but was just enough to keep dropping the level. i only noticed it when i was doing the front discs and pads.

a new pipe from ford was about 80 quid iirc but i just cut out the damaged part and put a bit of silicone hose in and it never happened again. and lasted another 2 years til i scrapped the car.

it's worth checking it just incase.