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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?
"why even though it was coolant it made the washer fluid light come on". The washer fluid system isn't tied to anything else, the only thing that is in there is whatever you (or someone else) put in there. The resevoir has a low level indicator and it really doesn't care what's in there, if it is below the sensor level it will turn the light on. On the topic of the radiator overflow tank, have you ever changed your antifreeze? Some of the long life AF's are orange, so turning brown isn't too much of a stetch if it hasn't been done in a while.
Living in Maryland, someone put antifreeze in the tank to do just that, keep the fluid from freezing. I would remove it with the warmer weather coming. The folks that live in our local mountains do the same thing in the winter. Living in So Cal, it doesn't get below 40-50 most winter nights.
Change your coolant every 2 years. It is cheap and the system (radiator and heater cores) will stay cleaner with less of a chance of gunk build up.
I would bet some one maybe a quick lube place put antifreeze in the wrong container by mistake .
Also all of the 1997-2002 range F150 and Expeditions have low level warning set way to hi they turn the light on when it is still half full.