The fuel gauge is not an equal linear measurement. You will find your answer by a simple math calculation. Take the tank capacity (26.4) x the calculated miles per gallon (mpg) lets say 14 mpg for this example. 26.4 x 14 = 369.6 miles per tank. Then, keep track of the gallons added on your next fill up when are near or at "0" gas gage reading. What you will find is that MB engineers have built in a "reserve" factor, so you do not run out of fuel. As a general rule, never run a diesel completely out of fuel. There is about a 20% reserve factor built in so you do not run out of fuel. Your reserve at "0" is 26.4 x 14 = 369.6 x 80% = 295.7. 369.6 - 295.7 = 74 miles in reserve.