There are just two many variables. Cleaning out the carbon is not going to be a bad thing though.


All 240ds do not seem to produce the same fuel milage. There is about a five miles per gallon varience. Many over the years have reported about 25 miles per gallon. While others reported in the 30 miles per gallon range. Just too many reports and I have never found a reason. The majority of these reports where posted by people with longer term ownerships.


Mercedes did some experimentation with the hole sizes in the pre chambers I understand. I do not know what reached production. A check of different part numbers for the pre chambers for different years may reveal something. If you can reach about thirty miles per gallon on the highway consider yourself fortunate. Many 240Ds cannot it seems. While many can.


It has bothered me for a long time as the five cylinder engines do not seem to have this issue. The non turbo charged five cylinder delivers less fuel milage than the turbo charged versions. Yet those that have added a turbo to their four cylinder 616s have not reported a milage gain. Yet on longer trips turbo or no turbo the cruise speed was probably similar. There is just something in this area with the four cylinder 616 I probably will never find if it exists.