As I review the board archives, I was struck by the number of posts regarding the recommended fuel octane rating for the S80 T6. Though the manual states that this engine runs best on fuel of 91 octane, my dealer assured me that mid-grade would be fine. I see that some T6 owners use the 89-octane fuel in order to save money and report that, despite some performance loss, their vehicles seem to run okay. After pondering the situation, I did some simple math. Please note that the assumptions used are my own and that yours may differ. In my area, 93 octane fuel sells for only $.04/gallon more than midgrade, but AAA says that the Texas average is $.08, so I’ll use that number. For the first 22,000 miles of its life, my 2001 T-6 has averaged 22.6 mpg. I buy new and never keep a vehicle longer than the powertrain warranty, so I’ll keep this little jewel a little over 4 years, or 50,000 miles. Do the math, and you’ll see that the total cost for using fuel on which the engine was designed to run most efficiently is $177. Please note that I am assuming identical mileage on each grade, even though on a 4-tank test I observed that 93-octane fuel delivered slightly better economy (0.2 mpg) and noticeable better performance than did the mid-grade. Since I paid around $4k extra to get the twin-turbo model instead of the 2.9 engine, $177 seems like a pittance to pay to enjoy optimal performance.
jack <><