Mid grade works fine in my '91 420SEL, I can use regular in the '88 420SEL with no appreciable difference. No knocking in either, ever.

There was a difference in mpg when "winter" blended fuels were used. Thank God! they've done away with THAT boondoggle!

"We are going to SAVE the WORLD by forcing you to use gasoline that results in worse gas mileage! Please pass the MBTE!"

Cheers!

(Well, except in "Nannyville", otherwise known as "The City that Works!", aka Portland, Oregon, aka "Sodom on the Willamette")

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'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435