I have a 2001 S80 T6, it says in the manual that it's designed to run on 91 octane gasoline, but 87 is the minimum requirement...
what are you guys putting in your S80s? I just bought the car and have been using 91... but if 87 works okay, i'll go with that...

From a response below:
Based on what you said I did some calculations.

1.30 gal reg 320/15 = 21.33 mpg
1.45 gal prem 360/15 = 24 mpg

24 - 21.33 = 2.67 mpg increase.

1.45 x 15 = 21.75
1.30 x 15 = 19.50

21.75 - 19.50 = $2.25 per tank difference

The cost to run the regular gas the (same distance) as the premium:

320 miles / 15 gal = 21.333 mpg, 360 miles / 21.333 gal = 16.875 gallons of regular to run the same mileage as premium fuel. 1.875 Gallons more.

16.875 gallons x 1.3 = ($21.9375) compared to ($21.75) to run premium fuel the same distance, or $.1875 more.

Huh?

Here our fuel of available in 87, 89, and 91 octane. The bp station has 87, 89, and 92, but their prices are high. One station has 105.

I've used 91 or 92 since I got the car a few months ago (it came to me with 44K miles). At most, it's like $2 more expensive per tank. Big deal.

ALL Volvo turbo cars require premium (92, 93 octane) OR your engine's performance will be less than optimal.

The owners manuel says 91 Octane.


It may say optimal performance, but can you actually see it?? I have yet to hear from anyone who has concrete evidence to support this.

20 years of hearing that from Volvo instructors in classrooms is enough for me. I own a turbo wagon and I never use anything but 93 octane, never have.
What I've always been told (and read) is that if one uses lower octane fuel in a turbo engine, it knocks (so slightly that you won't hear it but the knock sensor(s) does) and thus retards timing slightly lowering performance. It might be slight but why skimp on fuel when you bought the car for the added performance over a NA engine?
No, I have no immediate source of written proof but I believe it. Maybe 91 octane's OK but I prefer 93 and we're only talking pennies anyway.
Supercharged and NA high compression engines also require premium and always have.

I appreciate your explanation. I was simply told by many people that it wouldn't make a difference. I guess from reading your excerpt there is another truth.

By the way, they don't sell 93 octane in Denver at any station except one that I found and it is 93.5 octane. The rest sell 91 at best.

The ratings here are 85,87,91.
At sea level I noticed they were 87,91,93. Why the difference, I don't know?

Question for you then:

What would the difference in gas mileage be between 85 and 91, if you know?


Thanks

I don't know why octane ratings are lower in Denver but perhaps is due to higher elevations for mountainous driving? That idea also seems strange too as I've been in other western states with higher elevations that had 92 octane. Perhaps a CO thing?
So...91 then IS your best premium and should then be OK. I wouldn't use mid-grade or the lowest octane stuff in a turbo car but no, I've never checked mileage differences myself but another person (shown below) has.

better mileage with higher octane is true. a year ago i did an experiment with my previous Volvo, an 850. one tank full i put in 87 octane (lowest in Long Island, NY) and got about 320 miles for 15 gallons. next, i put in a tank full of 93 octane and got just a little over 360. keep in mind it was the same route driven and the same style of driving for those couple of weeks.
suffice it to say the extra mileage is definetly worth the extra cents on the gallon for premium.
i have also noticed that the engine was guicker to respond to my inputs and was also quieter with premium. this would have to do with the 'knocking' associated with lower octane fuels which was mentioned by someone else.

i hope this sheds some light.

Based on what you said I did some calculations.

1.30 gal reg 320/15 = 21.33 mpg
1.45 gal prem 360/15 = 24 mpg

24 - 21.33 = 2.67 mpg increase.

1.45 x 15 = 21.75
1.30 x 15 = 19.50

21.75 - 19.50 = $2.25 per tank difference

The cost to run the regular gas the (same distance) as the premium:

320 miles / 15 gal = 21.333 mpg, 360 miles / 21.333 gal = 16.875 gallons of regular to run the same mileage as premium fuel. 1.875 Gallons more.

16.875 gallons x 1.3 = ($21.9375) compared to ($21.75) to run premium fuel the same distance, or $.1875 more.

Huh?

My 850 recommends 91 also.

I live in Denver and have heard that altitude also affects octane lowering the requirement. I run 85 and 87 depending on how I feel at the pump. I don't notice any difference performance or mileage wise. Two dealer mechanics advised me to run at least 87 if not 91. They said mileage would increase.

Who knows?

Try several tanks of each and see how your car runs.