Wow, I have never gotten more than 28 from my wagon in any driving circumstances. I average 25-26 (and that is without AC). This has been the case for 40-50k. Vacuum lines have been gone through and are intact as far as I know.

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1987 300TDT - 195,000 (Original #14 head)
1993 190E 2.3 - 105,000
1981 300D - 250,000