Ive got an '81 300sd and I have only broken 30 mpg on a long road trip to Utah.
The mileage you are getting is pretty good. Ya gotta remember, these cars weigh over 2 tons. There are very few cars that are that heavy and get 25+ mpg.

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"spreading a trail of obnoxious where ever we go"
1981 300sd w/ 341,500 miles

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