Re: Recommended fuel for XC90 (kwald)
I believe the higher octane simply prevents knocking which can accelerate engine wear. The old 'rule of thumb' was to put in the lowest rating you could and still not hear any knocking.
I'm not sure about volvos, but BMWs will adjust to lower octanes. If the BMW engine detects a lower octane, it will retard the timing to prevent knocking - this prevents damage to your engine, but at the expense of efficiency and power.
Net-net, I think as long as you don't hear knocking you are OK (though you may be sacrificing power or economy).
I run 92 in the bimmer and 90 in the brick.
