If you want to stay within Ford guidelines, so your warranty isn't an issue, the ratio depends on what blend of Bio you can get.


If you can get:
B100 use 1/2 gal of BD to 9 1/2 gal #2
B50 use 1 gal of BD to 9 gal #2
B20 use 2 1/2 gal of BD to 7 1/2 gal #2
B10 use 5 gal BD to 5 gal #2
B5 Fill up the tank with BD

Of course if warranty is not an issue, because you already are over the mile limit. Just fill up with BD.