I dunno, Ethanol is supposed to be 10% less energy per unit than gasoline, and gas is supposed to have no more than 10% ethanol in the blend, therefore 10% of your fuel is 10% less powerful, meaning a total of 1% less energy in a gas-methanol blend of 90% gas 10% ethanol. In other words, in theory, you should only see a 1% drop in mileage with ethanol blended gas.

I'm beginning to think that perhaps something wasn't connected back correctly when the water pump swap was done. Perhaps a vacuum line? Maybe two were swapped accidentally and so everything looks ok? Kinda stabbing in the dark here.

Did you notice soot at your tailpipe? I would expect to see quite a bit of it if your MPG is really that low.

As for the odometer gear, if it's the same as a W126, it's not too hard to swap out by yourself, but I've never pulled a cluster out on a 124 personally.

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition