[Robu]

My fuel economy did NOT suffer rather I am getting at least 4mpg more with 89. can I say it was due to 89octane , No ! it might be due to engine been smoother after every mile.
I may try to fill couple of Tanks with 91 and compare again.

But I trust the BMW engineering, they must have tested the ignition and timing of Burning with each octane before recommending 89 . advanced timing of ignition by using higher octane doesn't improve performance - a fact.

it was bad that even the service engineer was outdated with BMW's recommendations.

 

[Robu]

I read somewhere that its more likely to have more ethanol % in Premium Gases because ethanol is used to increase the Octane, Gas station just mentioned Max Ethanol value and do not disclosed exact amount.

on St. Patrick's Day; Cheers to all fellow riders !!

 

[Robu]

I have been Using Shell but they have disclaimer that it may contain upto 10% ethnol. I have not noticed it on a particular section of octane but a general disclaimer. now how do I read this? I think they mean it applies to all octanes. Chevron does the same. when we say we try to find gas with no ethanol.. what do you read "ethanol Free"? in SolCal LA area, I have not seen any Gas station saying ethanol free anywhere.. but it would be nice to have enthanol free Gas because then Gas Octane Value wont change its properties based upon Humidity in air . I started caring for humidity in air since we are having few rains in LA lately LOL ;-)

 

[Robu]

whatever I read so far, high octane doesn't mean it wont gunk, its detergent/additives added in Fuel that cleans the gunk. All Chevron's and costco's fuels are added as many as 5 time the recommended value of this 'Detergent' at least so they claim. however in my CARS, I always add one bottle of Techron Plus after every 1000 Miles. Jim mentioned he uses BMW fuel cleaner. Is this same as Techron?

here are extract from Federal Trade Commission's website
Will higher octane gasoline clean your engine better?

No, as a rule, high octane gasoline doesn’t outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car's engine. In fact, the U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.

source --> https://www.consumer.ftc.gov/articles/0210-paying-premium-high-octane-gasoline