When I bought my '98 S70 (base, manual shift) , I used mid-level gasoline (89 octane) for the three years I drove it. Even though the manual called for premium gas, I experimented with 87 and 91 octane and the car seemed to automatically adjust the timing and run just fine. By that, I mean, I really couldn't tell the difference but I continued to use 89o.

Last October I bought my present '00 S70 GLT/SE (automatic) and, like the '98, it was delivered with 91o in the tank and the manual recommended 91o. This time, I used 91o for almost 4 months in order to get the full feel of its performance on streets and roads I travel daily. Then, I started using 87o thinking I would be able to feel the drop in performance in my normal driving after such a long time using 91o. If I felt the drop, I had planned to then try 89o for a while.

BUT, I felt no difference whatever in the performance. I decided to give it more time and the 87o usage stretched out to over a month. This light turbo adjusted to the lower octane like my base model did three years earlier. (My wife's '01 C320 Mercedes gives all sort of warnings about using anything lower than 91o. You'd think the car will melt in the driveway if you use a tank of non-premium fuel.)

With gas prices punching through the roof, I have stayed with 87o. I would use a higher octane if I could even say "I THINK I feel a drop in power or some other difference, but I can't. Has anyone else had this experience?

Jobe, I have a base '98 S70 5 speed and i have been using 87o gas almost all the time. I, like you, can not tell much difference (except $0.30/gal in my wallet) between the 87 and 93 octane. One thing, to remember, though is that premium gas usually (but not always in case of no-name gas stations) contains more detergents. This is the reason I regularly use fuel system cleaner (like Chevron or some other good quality stuff). This still comes out cheaper than paying for premium all the time. Most of the time you don't need the benefit of the premuim, but the gas companies' marketing has convinced most people that high octane gas is better (they even call it "premuim" when it is really a lower quality, more impure, not grade of gas that is hard to ignite). If your car does not ping or knock and feels like it goes good, use the lowest grade of gas that will keep it that way. This my rule of thumb. I used to have an Acura Integra that I fed 86 when I could find it (Sunoco's regular) and I sold the thing with 130k miles with engine running like new and not burning any oil and emmisions almost not registering on Massachusetts emissions test.

Let your common sense be your guide.

Good luck.

In my experience with my S70, octane ratings mean nothing as far as performance is concerned. The difference comes when its time to renew your emissions sticker. Though it wont become a problem for many years. After 6 or 7 I'm told, the low octane gas will leave sufficient deposits on your valves, etc. to cause you to fail emissions. This info comes directly from more than five emissions technicians. Stick with low test if you like, every 8 or 9 tanks however, load up with premium to clean out your valves, cylinders, and all that good stuff.

Seems more logical that the LOWER octane, with LESS anti-knock ingredients, which burns faster, and hotter, would leave LESS deposits. I think the only question remains whether one experiences "pinging", "knocking", or decreased power or performance.....

Dont believe the hype. Octane is in the same family as propane. It is an eight sided arcane. It is added to gas as an anti-knock agent. All things being equal the higher the octane the higher the temp required to ignite it. As I have said before, you can drop a lit cigarette in 130 octane and get nothing. Not even flash over. Once again, all things being equal, lower octane will yield better fuel economy and a cleaner engine due to more complete combustion. When you add other variables to fuel properties, like detergents, everything changes. So don't assume certain changes are due to more octane in the gas. This is simple chemistry. There does not need to be this much hype and mystery.

I dunno, Ian. A lot of posts have mentioned that your engine stays cleaner with the lower octane. Something about less additives and stuff to dirty up the engine. I must say that I have noticed very little difference, if any at all, between 87 or 89 octane. I seldom use 93. I live in FLAT FL so I might use a higher octane if I lived in very hilly or mountainous country and experienced 'pinging'.

Regards,

Eddie W. in FL

My 850 NA does not seem to make any more power with 91 octane. It does get slightly better MPG with the 91 octane though.............

Where are you guys getting 91 octane?

I see only 87, 89, and 93.

I do notice that you get more octane bang for the buck with

the 93 since you get 4 points for only a few cents, while the price difference for 87 vs 89 is more than a few cents.

Rich in NJ

I saw 91 octance in Canada. It was really cool, except they use liters. Wish they had that here.

My gas cashier gets confused when I tell her I'm going to stop at 5 gallons(89 octane), change over to 93 octane and add 5 more gallons. Hence 91.

I wish I had your luck. Every car I have ever owned has got better milage with lower octane.

This was true until the 855....it's a pretty small almost negligiable difference (hardly 1 mpg) and I certainly DON'T buy premium anymore.