Owner's Manual
Page 293
... for the 2500 and 3500 Series is from 0 to 1 5/8 inch (40 mm) below the bottom of the filler plug hole. If you have the 1500 Series, the proper level is from 5/8 inch (15 mm) to 1/4 (6 mm) below the bottom of the filler plug hole.
... for the 2500 and 3500 Series is from 0 to 1 5/8 inch (40 mm) below the bottom of the filler plug hole. If you have the 1500 Series, the proper level is from 5/8 inch (15 mm) to 1/4 (6 mm) below the bottom of the filler plug hole.