Since fuel has become SO high priced I went ahead and tried a tank or two of Regular 87 octane.

95' S420 (119 motor). I cannot tell one bit of difference in the way the engine sounds or performs. Mileage is still good (same as it was on 91 octane),
17+ in all city.
20+ on highway 70-85 mph

What components might be performing differently with regular grade fuel. I am real picky about how my car performs and I do all regular services myself.

How could I tell if anything is not OK. Every measurable engine parameter seems the same.
Engine temps,
mileage,
engine sounds,
idle characteristics and rpm,
oil pressure,
EVERYTHING !
I can't measure such stuff as cat. temps. however.
If there is any difference in power I can't tell it, although I have not tried any really high stress stuff like 1/4 mile times or top speed, But I don't know those with premium fuel anyway?

DanielW
95 S420, 82,000m (still on Starmark for 6 more mos.)
2005 Dodge Dakota 4.7V8
1987 FJ1200 Yamaha Cycle, 56,000m
2004 Acura TL, 9000m, (traded on the Dodge PU)(fast, but)
(I learned the hard way that I did NOT like FWD cars)
1987 300E, MB,210Km, (traded in on the S420)
1984 533 BMW, 220Km (Sold)
1979 320I BMW, 311Km (Sold)
1976 530 BMW, 170Km (Sold)