What type of Gas should Prius stay AWAY

In the 2001 to 2009 Prius, no better gas mileage was measured for any gas other than the 87 octane (from a reputable station) recommended by Toyota. There is some evidence that high octane produced more power in hill climbs.

Toyota still recommends 87 Octane for 2010. (there was a typo in early manuals that said 88, but that was an error) I have not heard that anyone has done exhaustive testing of other octanes in the new Prius.

(In mountain areas, 85 octane is OK)

 

You are not "treating" your car when you use higher octane fuel. In fact you could be doing more harm than good as the higher octane fuel is more resistant to burning and you may not get as complete a burn as you would with 87 octane. This would likely increase emisisons as well. The only time I would consider 91 octane on a Prius is if it had VERY high miles and required the higher octane to reduce engine pinging due to carbon deposits and such.

Higher octane fuel will not give you more power unless your car's anti-knock sensors are reducing timing due to preignition or detonation. This can happen on some cars when under load like partial throttle freeway merging (happened on my 2000 Corvette a lot) or on smaller cars when going up steep hills.

 

You can see the difference between 89 and 87 octane, E10 gas in a hill climb:


As a general rule:

• 87 octane - appears to have more energy per unit
• 89 octane - appears to handle very high power better

Choose the octane that matches your driving style.

Bob Wilson

 

Wow. I'm feeling really stupid because I can't understand that graph. I just woke up and am still a bit under the weather but even so... I really don't see how to get that info out of it.

I see that it says what the blue and red lines are, but I don't know what those mean. They don't seem to represent the 87 and 89 octane. So where do you see the difference in those?

I used to get 87 for my old truck but I filled up with 89 for my first tank thinking it would be better for my car.

 

It's not just you. It is kind of confusing because of the legend details. lol

 

In a nutshell, Bob found that 87 octane gives the best mileage, while 89 octane produces a bit more power. If you want to climb Pike's Peak in the shortest time, use 89 octane. If you want better mileage, use 87.

As for me, I recommend 87 octane unless you are driving at altitude, in which case 85 octane is recommended.

Tom

 

I'd be hesitant to say that it "produces a bit more power". The only real way to test that would be on a chassis or engine dyno (Dynopac or Dyno Dynamics units can simulate load characteristics) while monitoring igniting timing retard. This would allow you to determine where the extra power is coming from whether it be fuel energy content or due to an increase or decrease of ignition timing. On a properly running car you should not experience much ignition retard going up mild hills with manufacture specified octane. Since I don't think anyone has measured this in the 2010 Prius I'm not sure if this is the case and may be why Bob saw a difference between 87 and 89 octane.

 

Just drive it. It's not going to hurt anything. It's just a waste of money.

 

any octane higher than what recommended in the manual for the car is just wasting money. No need for higher than the regular 87.

 

Get a hose and start sucking.

 

I am a Chevron stockholder so if you want to pay more for premium, it is OK with me. However, as a Prius forum member, I would highly recommend 87 octane.

 

Higher Octane fuel is good if your car 'pings', 'knocks' or suffers detonation. It is both more expensive and has slightly less energy content than lower octane fuel. Some vendors seem to put more engine cleaners in their high octane gas. (or at least they word their ads to make it appear they do)

For this tank, you will get very slightly less MPG. Long term, use high quality 87 octane gas from busy stations.

And the only fuels to stay away from are not gas, do not use diesel or E85 in a Prius.

 

I thought I was reading the online dating discussion for a second.

 

There are some indications that higher than 87 octane may even be somewhat harmful to the fuel system, although using infrequently in an emergency, should be OK. 87 octane does have more energy than higher octane, and also burns more easily.

 

Me too. The first time I read that as "Get a horse and ..."

Tom