Charlie -
You have it! The city driving w/AC is where the fuel is going. If you'll recall, that's exactly what we found in controlled testing. If you were doing primarily highway driving you would see a different result. But in the real world I'd choose a couple of MPG over roasting in city traffic every time.

Dan

I seem to recall that's what Mythbusters concluded.

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Lots of diesel W126s in the past
Current: 1991 Toyota 4Runner with an OM603