The tank on the Mark III is 17 gal as noted. The fuel gauge and sending units are off on almost everyone that I have seen. When mine is FULL, the gauge reads between 3/4 and F, but it never gets to or goes past the F. When I am at 1/2 tank, my car takes 11 gallons.
The best way to meter your tank, is to FILL it, drive till 3/4, Re-FILL and record Gallons used. Do same for 1/2, ReFILL and record; and again at 1/4, ReFILL and record; then as close to E as you dare, Re-FILL and record. You will notice it's not linear.
That should help you gauge how much gas you've used and have left. (if you don't trust your gas gauge)
Francis
