I am having the same issue with my 2018 Expedition Eco Boost 3.5. Bought it in October of 2023 and in Feb the fan would not stop running. I noticed the a/c being warm and then temp was showing digits on the Eng Temp gauge on the dash. Got it home, and the reservoir was basically empty. Filled it up, all issues gone. Took it to the stealership, and they put it under pressure multiple times and never found a leak. Since they put me down the road, I have filled it up again since May at least 2-3 times. I suspect the water pump is where it's coming from under driving load.