Hi there,
It needs a tuneup real badly... my '79 450SL, which is essentially the same car, gets 18 mpg, after working on the warm-up compensator. The funny thing is that my '82 380SL, which has an '86 560SL engine installed, gets an average of 21.4 mpg. I suppose that's due to the better rear end ratio. Both cars are very fun to drive, but the '82 has much more power.

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C