mpg with 91 vs 87, in your prius c

...I am saying same thing Mahout is saying there could be variations in energy content (MPG), in non-reformulated gasoline areas. According to Chevron, and my limted sampling to date, there are no MPG advantages for Premium in refomrulated gasoline areas. In those non-RFG regions where there could be a MPG advantage for Premium or E0, it usually will not pay off. But as Prius owners sometimes we're trying to set personal records for MPG and miles/tank and we need to know how to max out MPG if we want to. Or if someone says they are getting 55 MPG on Premium, maybe its true. Not saying it pays off, just saying there could be variations.

The guys (and gals) on the website trying to get 800 miles/tank...they mostly know they need the best energy content they can get. Those in reformulated gasoline areas (such as Walter Lee of MD) know they cannot get the records and always ask for recognition of doing the best they could with lower energy content fuel.

 

Walter has Gen3 and OP has "C".. what is true for Gen3 may be different for "C" or for your Gen2.

I am curious enough to pay extra $2/tank at Costco (toptier) to try it.

Since energy content btw E10 and E0 3%, it would be unlikely that in case if Premium will have any MPG improvement it would be cost-effective. BUT $4-5 to test isn't gonna kill my bank account.

I will record current tank (87), two tanks on premium and then another tank on regular. Then average results. That way hopefully the impact of break-in and outside temperatures to which "C" is sensitive will be lessened.

 

I like tests...

 

Even though I am a noob here, I think I found the answer..... In the Manual.

I found on the Toyota's Owners web site.

In the 6-1 Specifications Maintenance data manual it states:

"Octane Rating 87 (Research Octane Number 91) or higher."

To me, that means that the car does run better on 91 Octane as they researched it with using 91 Octane. Maybe they have the computer tuned to know if it has a higher octane or its just designed to run better(more efficient) on 91 Octane.

Regards.
AJ

 

I am running the 87 vs premium test with costco gas too. Of cause we use different formula, so it is still not apples to apples. Stay tuned

 

IF they are controlled enough to actually have some validity.

 

Wrong. Absolutely wrong.
Cars that do run better with more octane actually SAY exactly that; you don't have to guess about it.
What that wording means is: You can run higher octane if you like wasting money and it will cause absolutely NO adverse impact on the engine.
That is ALL it means; nothing more.

 

They actually mean 91 RON vs 87 M+R (look MON vs RON in posts above)

 

At the Camaro5 sight a year or so ago they did experiments on 2010 V6 and saw no immedite difference but, after several tank fulls they put on a dino and there was a slight (can remember exact amount) consitant performance increase. The computer always seams to be testing the timing and it becomes more agressive with it over time as it sees no knock signal. In fact on the V8 they actually discovered by pulling two fuses after filling with premium the car would learn faster. SO if you are going to test this I think you will need to run several tankfuls thru first so computer adjusts.
I hope to by a Prius for my work car someday and will test this out myself.

 

I gave up after 1st tank.
87 - 456mi - 54.8MPG
93 - 450mi - 52.8MPG

OP reported immediate increase in MPG, and I am seeing opposite. Probably due to lower temperatures or just normal variations in driving. There must be something else going on; like his premium having different energy content, different gasoline formulation used, etc. Perhaps his engine has deposits and mine doesn't; as my "C" is still very new.

 

That doesn't apply to all engines though.
The "computer" has an upper limit to the timing advance it can apply.
Most engines that are designed to run strictly on regular gas will NOT advance the timing enough to take advantage of higher octane.

 

I once ran a tank of Costco Premium 92 octane (10% Ethanol in Oregon) in our 2010 Prius, I noticed no difference over Costco 87. I ran two tanks of 87 octane in our 2014 Volt which requires 91 octane. We noticed no difference with our Volt in mpg's or power. Premium gas is probably helpful in a high compression turbo charged engine, but not in a naturally aspirated engine as the Prius and the Volt....

 

I think GM spec's higher octane gas for the Volt though, don't they? It's not so much whether it's turbocharged or not, more likely to be compression ratio: typically higher compression ratios require higher octane.

 

I think the main reason for premium for the Volt is that premium gas as a longer shelve life than regular. In the Volt a tank of gas may be nearly a year old before the engines computer will start to burn it off and even premium gas after a year is probably 87 or 88 octane at that point.

 

ran 2 more tanks with 87.
MPG dropped to 338mi - 47.3MPG. On second tank it is going to be 48ish.

The difference in temperatures and driving patterns (2 snow storms we had) can be accountable for these changes.
Seat of the pants feel there is less vibration and more power with premium.

I will try premium again, but as is if there is any improvement it is not enough to cover $.25 price difference

 

Sounds like a long commute...do you think you get as far out as where they sell non-refomulated gaso? I can upload a map.

 

Map would be great, thanks!

Drove yesterday to and from work (17mi one way). Barely got over 50mpg on a way to, and was over 60 on a way home. Normally mpg 1-2mpg worse on a way home as there is slight elevation gain. So why so different? It was 45F in afternoon and car was parked in the sun; warm enough for heater to not kick in.

These tests are useless at least until it warms up and heater is not needed.

 

Don't discount wind speed and direction.
Aero drag, or the lack of it, is the single biggest factor in gas mileage at any speed over about 20 MPH.

 

Here is map of gasoline requirements (reformulated gasoline etc).
If you go to the LINK there is a very detailed PDF you can zoom into your area to see the county lines.
The is also an EPA web page that lists counties.
Well 17 miles probably does not get you out of the East Coast RFG zone

U.S. Gasoline Requirements