Type of Fuel

Most all motors detune themselves to inhibit knock electronically, so it is highly unlikely that there would be knock in any ICE, except under extreme loads on really hot days, and I am not sure if that is even the case anymore. Certainly with an Atkinson cycle motor, AND a CVT, I don't think the Prius mill is ever under significant load, even without the electric motor helping out. The opposite is more usually the problem when it motorboats into the rev limiter.

I did read that you should use the recommended grade, or at least always stick with a particular grade, since the knock sensor will get wacky if the octane suppression is raised and lowered. It thinks you are using the recommended grade and might throw a trouble code since it thinks there therefore must be something wrong with the engine.

I know you will get higher mpg and better HP out of a higher grade gas, but the difference it negligible. Certainly not worth the higher cost of the higher octane gas.

 

87 octane at lower elevations. In the Rocky Mountain States 85 octane will provide the same results because of lower absolute pressure in the combustion chamber.

 

I just tanked up at the rehab'd ARCO station here in Roseville. They have a interesting new policy, they only sell 91 Octane, at the lowest price. That is lower than their competition is selling 87 Octane for. My question: since the engine is designed for 87, will 91 Octane hurt it. ??

 

It shouldn't hurt a thing. Some have posted that mileage is less with premium, others say it is the same or better. I tried a couple of tanks of 91 as an experiment when I first got the car, I could tell no difference in mileage or power.

 

I use 87 octane for GenII, except made mistake last week, filled with premium. Hope it helped. I go with major suppliers based on various (grocery store, etc) discounts.

For the rest of world cases, the higher octane grade is interesting. I guess Volt needs premium (right?) so there are apparently ICE design decisions that can impact octane required. Also, Toyota recommends detergent additive, which overeas may requires high octane grade?

I got confused though Tofu, USA I think uses average (MON+RON)/2.
So when we say 87, that would about 91 RON.
According to Gen-II Toyota manual, use 87 Octane= minimum 91 Research Octane (RON).

 

Generally running the lowest octane the engine is designed to handle will provide the best performance and cleanest burn because it is easier to burn. Higher octane fuel is more resistant to burning which is why high performance engines with high compression and agressive timing charts require it. we have been led to believe high octane fuel will improve performance but that is simply not the case unless the engine requires it due to specs or your location and driving style dictates it, I.E. very hot temperature, low elevation, very agressive driving etc.

 

Trying to say USA uses Pump Octane = (RON + MON)/2
So correction to your math: 87 (RON+MON)/2 = approx. 91 RON
(per Toyota Gen-II USA manual)

So 95 RON = about 90 USA Octane (RON+MON)/2
MON would be about 85 in this example.

Typical Numbers
USA
RON 91
MON 83
R+M/2 87 (USA Prius Spec)

Aussie
RON 95 (Aussie Prius spec)
MON 85
R+M/2 90

 

Trying Shell only one time is not enough to give you information on how it does since mpg can fluctuate several mpg from tank to tank.

 

In Malaysia we have heavily subsidised 95 or less subsidised 97. About 30% diff in price. I am using the lower end one since no difference in the performance. between the two.

 

I live in Denver and our octane choices are 85, 87, or 91. I always pay extra for 87. Do you think I can use the 85, as stated in a previous post without hurting my engine?

 

I have been touring in the Rocky Mountain states (Idaho, Wyoming, & Montana) for the past few days. I have made a point of using nothing but 85 octane and the car runs great, my mileage has not taken a hit at all and may even be a bit better than usual.

I suspect that I tend to drive a bit faster than most Prius drivers and if there were problems I am convinced I would have noticed. Give it a try, it works fine.

 

In Denver, I don't think you'll notice any difference in using 85...and NO. It's almost certainly not going to hurt your motor.
If you develop knocking or pinging, you can always club back up to 87. Yeah....I know. Easy for me to say so since it's not my car.
If you're that worried about it....keep burning 87.

My bet: You aren't going to notice a bit of difference.

 

At high altitudes, there is less air to compress into the engine, so lower octane (and cheaper) fuel can be used. Go ahead and use 85. If you plan on driving down to sea level, you might fill up with 87, but if you don't, the car will throttle back it's performance to avoid knocking/pinging.

 

nice talking guys lolssss

 

This whole thing with putting up to 10% of ethanol in gasoline is BULLSH*T!!! I know it might be only a little amount, but ethanol actually decreases fuel economy compared to gasoline...I would happily spend an extra 20 cents per gallon if I could get 100% gasoline.
I wonder if there is a website that can help you find gas stations that don't add ethanol...I only use Chevron, so I bet that would be hard to find..if not impossible.

 

You can take a look at a site that I use a lot:

GasBuddy.com - Find Low Gas Prices in the USA and Canada

You can drill down to your state/city and there four columns where prices are listed for Regular Gas, Midgrade (10%), Premium, & Diesel Fuel.

Hope I'm not breaking any rules by inserting a link in here.

 

I will use 87 but since the newer Prius has a high compression motor (13:1 I believe) I would think it would benefit from a higher octane gasoline?

 

No because it is an Atkinson cycle engine. Effective compression ratio is 8:1. You are looking at the expansion ratio which is 13:1. Check out the links below.

Our Point of View: Atkinson Meets Otto: Why the Prius is So Efficient

Intro to Otto vs Prius Atkinson Thermodynamics

The car is designed to run on 87 octane so using a higher octane fuel will not increase performance except on steep hills if you are lucky and the car is retarding timing due to load.

 

Thanks for the great answer, F8L.

 

No problem, mate!