DIESEL FUEL ECON­OMY

Diesel Power - - Top Tech Questions -

QUES­TION: I have a ’17 Ford F-350. The truck has 13,000 miles on it. I see 14.3 mpg in town at 6,200 feet el­e­va­tion. On the high­way in Cal­i­for­nia, it gets 16 to 17 mpg. I hear re­ports of much more than that. Am I get­ting the mileage I should with a 6.7L Power Stroke engine? Is there any mod­i­fi­ca­tion I can do to im­prove mileage? The num­bers are for the truck empty with driver and one pas­sen­ger. Thomas Gold­en­berg

via email

AN­SWER: We re­ceive plenty of ques­tions re­lated to fuel econ­omy on diesels be­cause there’s not yet an EPA re­quire­ment to list mpg for heavy-duty (10,000-pounds-and-up GVWR) pick­ups. From our ex­pe­ri­ence driv­ing Fords and in do­ing com­par­i­son tests against GM and Ram pick­ups in the same seg­ment, your mileage is on par with the ex­pected fuel econ­omy for that type of ve­hi­cle. All the new­est ¾- and 1-ton trucks we’ve driven get be­tween 18 and 19 mpg on the open road (at 60 to 65 mph), 14 to 15 mpg in com­bined driv­ing, and 12 to 13 mpg in ac­tual stop-and-go city traf­fic. We test pump to pump, fill­ing up at the same fuel pump, top­ping off the tank, and then fig­ur­ing ac­tual mpg in­stead of us­ing OBD II data. Re­mem­ber, driv­ing at speeds more than 60 mph has a neg­a­tive ef­fect on fuel econ­omy. Aero­dy­namic drag in­creases with the square of ve­loc­ity, and with pick­ups, the ef­fect of drag re­ally shows it­self at speeds more than 60 mph. Fuel mileage can drop 10 per­cent driv­ing 65 mph in­stead of 55 mph. Lift kits and taller tires also in­crease drag as well as add weight, which also af­fects fuel econ­omy. In ad­di­tion to drag, engine rpm con­trib­utes to fuel econ­omy: Higher driv­ing speed and engine rpm yield lower fuel econ­omy. Eas­ing into and out of the throt­tle will give the best mileage. There are a lot of vari­ables. How­ever, the zero-cost way to im­prove mpg num­bers is to slow down on the high­way and reg­u­late the mod­u­la­tion of the right foot.

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