Compare apples to apples in regards to fuel economy.

What was the average mpg for the same chassis, same displacement gasser version Mercedes.

The actual mileage figures are very good. Mercedes in general, are gas hogs. The older ones are big, stodgy cars that have a lot of weight to throw around, and a lot of drag to overcome at high speeds. That's just the price one pays for driving an old German tank. Tanks are not known for efficiency. Their strengths, however, are much more obvious.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)