I know Toyota recommends no more than 87/89 octane in the tank. That is what I've always used. But here in Phoenix, when the summer temps get quite hot, and using the A/C is a fact of life, I've noticed somewhat sluggish performance while running around. Yes, my mileage is still better than average, but still sluggish. I know the engine has an engine knock sensor, that used with the engine electronics, will retard the ignition timing when it sense knock occurring. This in turn will also drop performance, or 'pep.' So I got an idea at yesterday's fill-up at the gas station. I decided to pump 89 octane instead of the usual 87 that I always pump. This was at the same station I always buy gas from, so I'm not mixing brands here. All afternoon yesterday (the temp was 109), last night (the temp was 100), and now this morning (the temp is 87), I've notice a predictable increase in performance. But what was suspected, was also an increase in mileage gain. That is, I've noticed while using 87 octane, I would have to push the car harder to achieve acceleration I desire, and mpg gain while cruising at the 'sweet spot' was very slow. But with 89 octane I don't have to push it as hard, and the mpg gain while cruising is much quicker on 89 than on 87. So it seems running 89 octane must reduce knock potential significantly, thereby allowing the ignition timing to remain where it needs to be, thereby keeping the performance that Toyota desires. I don't think the extra 2 octane is going to hurt anything (other than my pocketbook a bit), but what do the Prius Pros here on the forum think? I surely like the performance gain and I will switch back to 87 octane when the summer wanes again.
A one-time sample is hardly conclusive. This is a very old argument, and nothing has ever been proven one way or the other.
Confirmation Bias is a real thing. More performance from higher octane, not so much. (you are, of course, free to spend more for gasoline) Also, what is true in Phoenix, may not be true else where "Hot temperatures and exceptionally low humidity can increase an engine's octane requirements as well." - Test Results They found no real difference in cars designed for regular with modern electronics, but they did not test in Arizona.
You'll need a proper ABA test to corroborate your claim. Edmunds did a similar test on a turbo charged Chevy Cruze that supports your theory. The Ultimate Hot Weather MPG Test - Regular vs. Premium - 2011 Chevrolet Cruze LTZ Long-Term Road Test They even went through calculating the extra cost on the increased fuel economy which made the 91 worth it.
There's one detail in the low-versus-high octane debate that is often overlooked and that is the ethanol content. This is a crap dilution of fuel, due to its lower BTU content, and will affect your MPG. I lost up to 10% on my V8s when my favorite brand started using ethanol. Found another brand with ethanol free 91 and my mileage came back... especially notable on my 2006 Charger Daytona that I previously ran on 87 or 89 (as per the manual). Cost wise, that same brand sold their 91 at 89 prices on Thursdays so it was overall a win for me (well, a recovery from a loss... I'd still want ethanol-free 87). Too soon to tell how my '12 Prius wagon behaves (just got it in late November) but I did seem to get a great mpg on a tank with half 87 and half 91, give or take (with the 91 being ethanol free).
We've discussed gaso grades quite a lot. Keep in mind the situation is different in different countries. Unfort in the USA we have 10% ethanol mandate which means many cannot get E0, and those who can get E0 it is quite expensive and rare to pay off. Also we have RFG (EPA reformulated gasoline) rules that basically removes some of the energy content out of all grade including Premium. So I would like to try your 91 Octane E0 but we cannot get it here. There may be a few rural U.S. areas with cost-effective E0, but not for most of us Prius owners. We are expecting 3% less MPG for E10, just based on energy content calculations. In your case the Premium E0 could have more than 3% more energy if the base gasoline is better too.
Here in the US, E0 appears to be 50 cents a gallon higher than E10. I am not sure of the octane, but it is likely 87. For the US & Canada, you can search at Ethanol-free gas stations in the U.S. and Canada
SO.....for the increased mileage to actually be a winning proposition......at $3.00 a gallon for regular, your E0 fuel must give you a 17% gain in mileage or else you are actually spending more money overall. Highly unlikely that you will get anywhere close to a 17% increase.
Yes.....SO ?? The point IS: Do the math before you decide that you are doing something great by paying extra for E0. At that price point, if E0 is still $.50 more, you would need a 23% mileage increase to break even. It almost NEVER is worth the extra money.
The Edmunds.com article I linked above adds a data point that high compression turbo engines which has become more mainstream as of late may be retarding it's engine timings so much that fuel economy suffers. That's why the E0 91 is worth the cost over E10 87. Usually turbo engines require premium fuel as the high level sport trim offering. But now even a low trim level Cruze has a turbo engine and we 'mer'cans ain't payin' for no stinkin' premium.
For me, the important motivator was the Thursday "same as 89 octane" sale price on E0 91 octane. The recommended grade for my '06 Daytona Hemi (and now' 16 RT Charger) is 89 with 87 acceptable. So for those cars I'm essentially spending the equivalent of 89 if I only fuel up those days. For my Trans Ams it's 91 anyway so not an issue. I also don't trust that ethanol doesn't mess up things on engines that *should * be ok... I've seen photos of some nasty gas tanks due to all the water buildup. No thanks. Just like our '08 Civic I don't foresee treating the Prius as a collector car (although my OCD still commands me to treat it continuously like a new car even at 65k) so the 87 vs 91 E10 vs E0 thing is more of a scientific curiosity more than anything. As mentioned, so far a 50-50 mix has yielded an obvious bump in mpg given similar conditions but too soon to really tell due to constant temperature variations etcetc.
Sounds good to me too! I would also use it, sounds juicy I would expect better MPG. Unfort in USA it is largely unavailable especially at competitive prices.
