What octane to use?

[IdahoBob]

1) Between the 4 XC70's ( 2X '02, an '04 and an '06) we are running (me, wife, 2 kids) and the 2.9l non-turbo S80 I sold 4 months ago, we've probably run at least 520,000 miles in the past 7 years. All of this on 87 octane. No problems. The European octane count method and the US octane count methods are different. Our 87 is the continent's 89, just to confuse things. Our '98 Volvo's owner manual said to use 89, which I did until I noticed that the manual referred to the European calc. This same confusion could be the source of what someone is advising you.
2) If you can find non-alcohol regular, it's worth a few extra cents/gallon. My cars get approx 6-8% better mileage on pure 87 gasoline (no ethanol), and the fuel pump is quieter as I go down the road. One my engineer friends says that noise is a form of lost energy. Also, water in fuel isn't as viscous as pure gas; so it's more corrosive to components.

So, I buy the no-alcohol 87 when I can get it, and run the 87 octane all the time.

[Tonyx]

Little correction as I've worked with fuel before; US 87 regular, aka, 87 AKI is equivalent to EU 92 Octane fuel. The AKI is MON+RON average with 5 pt spread. So 87 + 5 = 92.

[zanzabar]

I know this thread is a few months old, but it's been 100 degrees plus for several weeks here. My 2001 V70 2.4t was running horribly. I put some 100% gasoline 91 octane in a nearly empty tank and it ran like a different car after a few miles. It had even stalled on me earlier in the day after backing out of my driveway. So, there could be a hundred different factors involved, but I think the 10% ethanol that's in all the gas around here is partly to blame, and high air temps just make it worse. I really hate to pay for premium or even 100% gasoline (vs. 10% ethanol) - so, I'll probably try to switch back to normal 87 octane when the air temps come down and see what happens. I've also considered just using Lucas Oil in every tank of regular 87 octane.

Your stalling and bad running issues are not related to octane or ethanol, more likely a real issue with fuel pump or pressure regulation.

I just drove across the midsection of the country and used several tanks of 10% ethanol gas. There was maybe a barely noticeable difference between that and 91 octane 100% gas at hard acceleration and driving up mountain passes. More likely it was all in my head. MPG also did not differ between regular, premium, or 10% ethanol.