I ran my 1985 300d on uvo/B-99 blend for 25,000 miles on my unmodified 300d. (yes it is warm down here in Florida) Only issue I had was short life of the pre-fuel filter(started using $2 clear ones at Walmart). Ran like a dream!! I just sold it last weekend and picked up a 1984 300d that I plan on running uvo in. By my calculations I am spending in fuel aprox what someone driving a car getting 60mpg would spend. I do not see a down side in these old mercedes!!

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2006 Jetta TDI DSG 320k miles
1997 Ford F150 325k miles 4.2L V6 "Work Truck"
2008 Tundra 225k miles 5.7L
1982 240D.....sold
1984 300D...Totaled OUCH!
1985 300D Turbo 222k miles "Dos" sold to 79Mercy
1986 300SDL 98K miles "The Beater"....sold
1987 190E 2.3 16v Euro spec 115K miles....sold