[diesel_mercedes] 350 SD Mileage

 

A couple days ago a member posted that he calculated 30+ MPG for a 350SD. I have a '91 short body; my mileage on long-distance road trips rarely exceeds 26 mpg. That's at 5 mph over freeway speed limit, steady state with cruise control, for thousand+ miles. My calculation spans several fill ups, which compensates for variable top offs at intervening stops.

My '81 300SD rarely exceeds 27 mpg, same conditions.

I've noticed a roughly +3% calibration error to both cars' speedometers compared to GPS, so my MPG is overstated by a like amount.

How on earth would I get 20-40% additional mileage? Two answers obvious to me are: shed excess weight (like gutting the interior) and reduce rolling resistence (running on high-pressure, skinny tires). Oh, and setting the cruise for 40 mph for lower drag.

Is my car flagrantly out of tune on fuel/air mixture? I don't have soot belching out the tailpipe...

The car's PO had the notorious 3.5 L diesel replaced courtesy of Benz, thank you very much. But I assume the fuel injection has 189K chassis miles on it and I've never touched it.

MKJ

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