My 1986 300E has suddenly had a drastic drop in gas mileage. I generally get 18-20 here in Maine during the winter, but I am now gettted about 12-14. The car is running fine, no hesitation, starts easily etc. I changed the plugs about 3 months ago, and cleaned the distributor contacts and rotor at the same time. The air/fuel milture was set at taht time too. It almost seems like there may be a fuel leak? If this is NOT the problem, then why the sudden drop in mileage?

most will probably say o2 sensor..

that seems like a huge drop, however.

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


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I second the O2 sensor. Although completely different cars, I had a 92 Buick roadmaster and a 88 BMW 528E. Both had there mileage drop into the teens and an O2 sensor brought them back up. Neither displayed a check engine light.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes

Thanks for the help on the gas mileage problem. I will check into getting an O2 sensor. Any idea what one will cost me on the net? Should I look for a used one or buy a new one? I KNOW that the sensor has NOT been changed in the 8 years that I have owned the 300E!

you might want to get the lambda adjusted in your fuel system adjusted. Had the dealership adjust the lambda ratio and the car runs like its brand new and much improved gas mileage. Also you may want to replace the fuel filter in tank screen. A dirty or clogged one will cut down on the gas mileage. Also check the obivous such as 02 sensor, fuel filter, injectors etc.

Hope this helps

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

Get a new one. They are not all that pricey. They are good usually 50-75,000 miles.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes