What gas do you use?

I use E10 94RON or 95RON

 

I also use regular 87. Works good for me.

 

87 is the best for the Prius.

It's hard to gauge if a higher octane benefits the prius by checking your MPG with so many variables to account for, but generally lower octane gasoline has more energy. The only real benefit that the higher octane gas will provide is that the Super (most expensive 92, 93, or 94) usually contains alot more cleaning additives from whatever chain you buy from. Also if you didn't know the gas station only sells two grades of gas, all the middle grade(s) (usually 89 and sometimes 91) is just a mixture of the Premium and the Regular.

 

I should add, the E10 I use comes as a liquid not a gas.

 

I pushed the 89 button by mistake a couple of nights ago, and I swear the car feels quicker. But then, I also like my BT brace and my sharkfin. Must be placebo effect! I've used mostly Shell, Costco or Chevron 87 for over 50,000 miles now, and this is my first 89. Your mileage (or placebo effect) may vary.

 

I have an '07 Prius. I had been using Exxon and was satisfied with 45-50 mpg. Then a funny thing happened. New gas at Exxon a couple of weeks ago, and it went to 35 mpg. I went to Toyota and told them there must be something wrong, maybe one spark plug failed? I had needed a checkup anyway, and they did it. They found nothing wrong. I thought "well here we go again with them not finding what's the matter". They told me there's a fuel addition gas companies use in the colder weather. It should take down my mpg maybe 5%. Well I got my Exxon gas again and again, and it stayed at about 35 mpg.
Then on a trip I needed gas. Amoco was there and I filled it up. The mpg returned to 50 mpg.
I figure I got bad gas from the Exxon stations nearby my house. And I figure they gyped me out of about $30 for 3 fillups. No wonder their chairman retire with a package of $600 millions.
Where do I get my refund?

 

87 octane E10 here in Phoenix. I get it at Costco.

 

Plain and simple for me....87 octane. I bought the Prius to save $ on gas, so there is really no need for me to buy 91 octane.

 

87 seems to be working just fine for me.

 

Lower octane fuel has less energy. Higher octane fuels have more energy, not intrinsically, but because of their formulation, including the additives.

The reason that they have more energy is because of their higher anti-knock properties, a higher ratio of carbon-carbon bonds to carbon-hydrogen bonds than low octane fuel. The carbon-carbon molecular bonds release more energy than carbon-hydrogen bonds upon detonation. See Octane rating - Wikipedia, the free encyclopedia

That's why race cars use high octane fuel. More energy per fill up. More energy for weight.

As for whether you should use it in your car, Prius or otherwise, it depends on whether the ECU detects and makes use of it. If it does you may a) get more performance, and b) better fuel economy. However if the car is not programmed for it you may not get any benefit at all.

In my car (not yet a Prius ) I get a moderate increase in fuel economy with high octane fuel, about 7%, which is in line with the information available from oil company web sites.

BTW For those don't know, when quoting octane numbers, be aware that there are two differing systems: the M.O.N. ratings used in US and Canada and the R.O.N. ratings used for most of the rest of the world, including Europe, Australasia and Japan.
Although not an exact equivalent, a rough rule of thumb is that
87MON equates to 91RON,
89-91MON equates to 95RON,
93-94MON equates to 98-100RON

So when reading posts about octane keep in mind where the poster is coming from, especially when talking about "91 octane" where the two systems overlap.

 

That's not what the Wiki article cited says.

Higher Octane = Higher "ACTIVATION" Energy, which means it ignites at a higher temperature. Therefore it won't pre-ignite in a high performance engine.

Octane has NOTHING to do with the amount of energy per unit volume.

Some High Octane "Premium" gasolines may have more energy per unit volume than their lower Octane counterparts, but that is only because the manufacturer chose to make it that way.

In no way can you assume that all high octane blends have more energy.

And, if Ethanol is used as the Octane booster, you can be pretty sure that the reverse is true and the lower Octane blend has more energy per unit volume.

In the past, analysis has shown that the in the majority of cases, the lower octane has higher energy density.

If you're going to bet with out knowing the specific manufacturer, I would lay good odds that lower octane = higher energy density.

 

What he said. Octane has NOTHING to do with how much energy gas has; it is only a measure of how much it resists preignition. Because of that, I would think that the lowest octane you could use without the car's ECU retarding timing because of knocking would deliver the best mpg.

 

Digging up old posts... see this post I started after attending a talk from a local gasoline distributor...
http://priuschat.com/forums/prius-main-forum/30900-truth-about-gasoline.html

 

All I know is this...

2002 Jaguar X-type asked for 91, I accidentally put 87 in and the crispness in acceleration and power was gone. Never did I make that mistake again.

1983 Jaguar XJ6, the service guy said 87 always, I tried 91 once or twice and saw no difference so 87 it was.

2007 Prius owners manual states 87 and that's exactly what I'll give it.

In 2005 I took a vacation to Ireland and rented a Toyota Yaris, not sold in the US at the time. Everywhere we went it was 98, no multigrades. That car went across country twice on a tank of gas, or petrol for you Euro types. We did some math, converting KM to Miles and Liters to Gallons and figured we were getting, consistantly mind you, 60mpg. Now fuel costs were converted too and I think it was in the neighborhood of $5.80/gl. I was glad to see the Yaris make to the US, had a great time in that little car, but the EPA MPG got me confuddled. Then I remembered the octane rating in Ireland and figured it was de-tuned to conform to US emissions standards. And yes, from Dingle to Dublin and back, 1 tank of petrol.

 

I just got an 08priusand the dealer says it requires premium. I looked at the manual, and it said the same thing. Did anything change......please let me know, or am i just reading it wrong.

 

2007 manual pg 320

Select unleaded gasoline with octane rating 87 (RON 91) or higher

Use of unleaded fuel lower than 87 and it may knock.

paraphrased

 

The Prius is very strange indeed how it manages different octanes. When I first got my 07 I was putting in 93 octane for about 2 tanks. The car ran really strong and had excellent performance but poor gas mileage. I learned on this site and the owners manual it prefers 87 octane. After its first 87 octane fill-up 5 miles down the road the ecu detected its octane and I instantly gained 5 mpg's on the mfd. Freaked me out. Performance suffered slightly compared to the 93 though. I have bypassed the hot water to the throttle body and that has restored alot of the lost pick up.