I am posting this here as it is in reference to the 5.4 motor but in a 2001 Expedition. I also posted it in the Expo forums. Any help would be appreciated:

My wife was driving our 2001 Expo the other day and the warning light came on that the windshield washer fluid was low. When she got home I popped the top the re fill the washer fluid and there was what appeared to be green coolant in the reservoir. It even smelled like coolant. It filled the reservoir about half way which made me wonder why even though it was coolant it made the washer fluid light come on. I then checked the coolant reservoir and it had fluid in it but it looked brown and nasty. The motor is the 5.4. Any ideas what is going on?

 

Possible that someone maybe mistakenly put coolant in the washer tank? I do not see how anything could get in there unless someone put it in there. I would drain the washer fluid tank and refill it with washer fluid and keep an eye on it just to be sure. The brown colored coolant could just mean that it is pretty old and dirty and time for a flush and change.