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Discussion Starter #1
Just curious if any other people out there are shelling out the extra $ for 91 octane fuel? My prius hasn't had anything but 91 and my theory is that it will run better and possibly use less fuel. I could be wrong and don't really know if it matters at all. I noticed at idle when I'm waiting for a red light the car almost shakes a bit sometimes as if the car was spitting exhaust out intermittantly. It only happens once in awhile but I'm curious if anyone else is using the 91 octane fuel and getting the same behavior. Does anyone know if this is normal? This car is so cool that nearly everyone I talk to is interested in it, I love my greenmachine.
 

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In my '03 Prius I used to put only 91 in the engine thinking that it would run cleaner, more efficiently, etc... However, I called the dealer and they said that 88 is the best for the Prius. (New Mexico has 86, 88, 91 because of the high altitude) The dealer was right, in fact, the mileage noticeably increased once I had lowered the octane to 88. In the our '04 Prius, I use 86. (Low altitude equivalent to 87). The mileage is noticeable better than 91 as well (49mpg vs. 43mpg). I buy the gas at Costco, so overall I usually spend 12 dollars for 400 miles. Use the 87 octane, you will get the best mileage, and spend the least amount of money.
 

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87 octane

The Prius Owner's Manual states to use 87 octane gasoline.

Several owners of the classic Prius have had check engine lights (engine misfire error codes) from using higher octane gasoline. (The 2004 Prius has the same engine.) The Prius' engine is not tuned for the later-igniting high octane gasoline.

Higher-octane gasoline actually contains less energy (BTUS) than regular-octane gasoline. Unless you have a car which is pinging, or it can change its timing based on the grade of gasoline, you will not receive higher MPG with a higher-octane fuel on a car designed to run on something lower.

I highly suggest that you read these publications from the US Federal Trade Commission:
The Low-Down on High Octane Gasoline:
http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm
How To Be Penny-Wise, Not Pump-Fuelish:
http://www.ftc.gov/bcp/conline/pubs/alerts/fuelalrt.htm

If you live in high-altitudes, you can probably get away with using 85 octane. If your only choice for low-sulfur gasoline in your area is to get the high-octane fuel, then perhaps the trade-off in MPG is worth the lower sulfur content (less damage to your catalytic converter).
 

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Several years ago (7-10) there was a big study on this and all I remember is 87 octane is fine for 99% of autos. It is a waste of $$ to purchase the higher octane. Not sure if this is true for higher elavations.

04 Salsa Red
 

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Don't run higher octane in your Prius thinking you are doing your IC engine a favor - it isn't helping at all. The IC engine in the Prius hardly has need for additional octane since it is complemented by a high torque electric motor. Increasing octane only helps when you have a higher than desirable amount of compression in a combustion chamber and the potential for pre-detonation is increased. Pre-detonation can destroy pistons (blow holes in them) and weaken or destroy crank-shaft bearings.

Octane additives retard the potential for the petrol to ignite without the spark of the plug - that's all.
 

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fuel with additives

Ok...how about lower octane fuels with additives? For years in my Volvo I used Chevron fuel with Techron because a mechanic said the additive would help keep the injectors clean. Would this also apply to hybrids with tricky anti-pollutions components?
 

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Re: fuel with additives

leebek said:
Ok...how about lower octane fuels with additives? For years in my Volvo I used Chevron fuel with Techron because a mechanic said the additive would help keep the injectors clean. Would this also apply to hybrids with tricky anti-pollutions components?
all gasoline intended for car consumption
have additives for cleaning and reducing
emissions. different names/products, but
they all do the same thing. (It's
an EPA thing.)
 

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It's surprising how few of our Prius group appears to have read the manual that comes with all the vehicles. It's ok to fool around a little bit with varying octane ratings in other vehicles, but it's an absolute no-no to do the same with the Prius. The Prius uses an extraordinary power plant in many ways and one of the ways it is different from most other cars is its use of VARIABLE VALVE TIMING. This shouldn't be confused with variable ignition timing. Practically all cars use variable ignitiion timing. Variable valve timing enables the Prius to burn fuel cleaner when the engine has not yet warmed up and then after it arrives at the proper engine temperature, burn the same fuel even cleaner. The Prius engine operates at an effective compression ratio of 13 to 1 and burns only 87 octane doing it. Other cars cannot do that! Please, do what the manual said to do. BURN 87 OCTANE FUEL! If you don't, sooner or later you're going to wind up with serious engine repairs. That wouldn't be fair to the less fortunate people who can only buy their vehicles in the used car market. :cry: Whatshisname
 
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