I lent my brother my '80 300D while he was visiting from the other side of Oz. He drove about 700km and returned better than 10 km/litre. (He actually said that hegets more than 100km for $10, but as diesel is >$1.00 per litre, I reckon that 10km/l is close)
That relates to 28.3 imperial MPG (US gallons are smaller) All this on a 380 000 km engine.

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.