The 240D has a bunch of engine roar at highway speeds 70-75mph. Usially so much so that I can't or don't want to turn up the Becker loud enough to overcome and add to the cacaphony. The 300SD idles louder than the 240D but I think that's because of the higher pressure injectors and an addtiional injector. At highway speeds it's quieter than the 240D but not as quiet as my Honda.

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Fred Johnson
1977 240D
1983 300SD