One thing I've always taken note of is the unique smells of different engines. My Benz's, my old Powerstrokes, the different Cummins (we have 5.9 common rails and 6.7's at my work), and the Duramax. They all smell a bit different, with the biggest changes being in correlation to the technology they use.

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1981 300SD - 283,000 KM's at purchase, 360k+ now. Engine replaced at 311k. 16" CLK wheels, w126 gen II cosmetic upgrades, late w126 leather interior. RIP. Parted and gone due to fire

1987 300SDL - 243K miles and counting. In winter hibernation!

2001 Ford F250 Super Duty "Platinum Edition" Lariat 4x4 7.3L turbo diesel, 295k+ miles, various mods for reliability and performance.