Is extran octan is good?

Higher Octane fuel will not help your mileage. It actually contains less energy than Regular, and is more likely to decrease your mileage.

It also burns slower, and can result in un-burnt fuel getting out the exhaust, which will at best pollute more, and at worst shorten the life of emissions components. Long term use can also cause carbon buildup on valves and such.

Because it's not burning as fast, or as completely, you will in fact have LESS power available too.

Toyota is very clear on using only Regular. Consistent High Octane use can result in an "Emissions System" warning light coming on because of the unburnt hydrocarbons.

One tank won't hurt you, but it's not something I'd do on a regular basis.

 

The extra push offered by premium fuel is probably psychological. Regular gas works just perfect and is cheaper.

 

Let us clarify that we are only talking about small, naturally aspirated 4 cylinder engines. It is not recommended to use high octane gas in a 1.5 liter, 4 cylinder engine. On the other hand, high octane gas is necessary to get the most power out of most 6 cylinder, V-8+, and all turbocharged engines. I know for a fact that with Saab, if you have engine problems, the technicians take a fuel sample and send it to a lab. If it's not 91 octane+, your warranty is voided. High octane fuel does have it's place...

 

There was a long drawn out discussion of this very issue with multiple authoritative citations in another thread on this board. (Maybe, someone remembers which.) Bottom line, higher octane has lower energy, actually burns somewhat slower and colder and can even do some (minor) harm to the Prius engine by encouraging buildup of combustion byproducts in the cylinders.

(If I have time later, I will run a search through the board)

Jon

 

High octane - wish I understood it better

I have heard essentially what Tempus is saying. However, I accidentally filled up with 91 octane about a week ago (bad habit from my previous car, a VW turbo). Well, I went 564 miles and it took 9.6 gal at my next fillup - 58.7 mpg! The screen was showing 56.4. My previous tankfull was 49.5 mpg. I didn't change anything about the way I drive, and I pretty much just commute back and forth to work and run a few errands. Could be just a coincidence, but it doesn't support the theory about high octane. I am now back in the low 50 mpgs with 85 octane. It's enough to make we want to try it again, but I don't want to damage the car.

 

Kingofgix,

Just a coincidence, try and search out the other thread I mentioned. Current tank running at 54 mpg with 87 octane 10% ethanol mix (slightly lower milage but burns even cleaner)

 

Colorado gas

In Colorado we have 85, 87 and 91 octane. i have been using 85 except for the one tank where I used 91. I got about 10% better milage on the tank with 91 octane than any other tank. I do, however, believe the general thread that high octane gas shouldn't improve milage, but it was a curious result.

 

i had to do a lot of searching but in my owners manual for my 1987 Corolla, it also required premium gas. (i never once put premium in it the whole time i had it) and its a 4 cylinder.

 

My salesman in Denver said to use the 85 octane.... checked with him as the car came with a full tank and I hadn't gone with them to fill the tank.. he also had no preferance to a brand...

 

This is another difference between U.S. and Europe. 95 Octane is the low grade fuel here. There might be some 93 Octane in some places but not around here. 98 Octane is used for high performance cars.

/Paj

 

well 87 is the lowest you can get in WA. i wonder if your 10% increase had to do with the gas you used, or the pump you got the gas from.

i am conducting experiments on the accuracy of gas pumps against the accuracy of the on board computer. although i will need 4 more tank fulls before i can begin to offer a hypothesis, i am suspecting that the difference between fillup mileage and computer mileage has to do with the pumps being inaccurate more than the computer always reading high or the bladder changing sizes.

the greatest difference ive had in mpg's happened when i used a certain pump. i reported it to the bureau of weights and measures, and they said that they will inspect and let me know if the pump was off although they cannot comment on whether the pump is for or against me and how much so it was either way.

in a way, im finding serendipedious ways of analyizing fata that has opened my eyes to different possibilities.
one of the things i recorded was pump # and location of the gas i got. this was in response to a news show segment detailing findings that 11% of WA St gas pumps are inaccurate. each day 15,000 gallons of gas are paid for but not received in this state.

couple that with an average inspection date of the pumps being the year 2000. (the newest inspection date is Nov 2000 the oldest being july 1999)

for all of you that got higher mileage on a tankful. if you can remember or have the chance, try filling up with regular at the same pump and see what your results are. this will probably only work if you track the previous fillups along with the fillup afterwards to eliminate variations in the bladder fillup. in my 7 fillups i have had 4 that where the computer was higher and 3 where the pump mpg was higher. so it DID even out to the computer overall mileage being .8 mpg higher. but then i had the one tank at the station i mentioned and it had a difference of 3.8 mpg (55.2 computer to 51.6 pump)
i had expected a slightly lower pump average since the previous tank was reversed (55.13 pump and 53.5 computer) but the 3.8 mpg difference was twice as large as any other reading so i suspect the pump.

 

What has gone before about octane and the Prius

The previous thread that I mentioned above that contains all you ever wanted to know about gas octane ratings, octane facts and myths, and why one wants to follow Toyota's recommendations about using 87 octane gas is contained here: High Octane Gas

Might prevent some rehashing of ground previously covered :mrgreen:

Jon

 

according to the U-W chemistry department.

in the state of WA there is only two pipelines bringing in gas from out of state.

ALL regular grades of gas are the same (Exxon, Shell, etc). Premium is created by including an additive package. Premium does not have lower sulfur content or lower anything for that matter. things that are added to Premium enables it to burn at higher compression and heat levels. reduces backfires, etc.

since the additives are added at distribution center to the basic regular gas, each brand is different at the premium level.

also some things to keep in mind, those two pipelines also bring in fuel oil, diesel, etc. there is some mixing of product. generally speaking, the volumes involved makes the risk of damage to your engine small. but its this that accounts for an estimated two-thirds of fouling in injectors. (along with contaminents... gasoline will absorb contaminents out of the air if left open to the atmosphere.)

also using high octane gas in a regular car, will basically only damage your wallet since the additives dont really do much anyway... the premium label is mostly hype.

 

The 2006 manual states " Select unleaded gasoline with an Octane Rating of 87 or higher.

 

The 2006 manual "Select unleaded gasoline with an Octane Rating of 87 or HIGHER.

 

Using gasoline of a higher octane rating can also damage your emissions system over a period of time. You don't get better gas mileage with higher octane rating. Use the recommended octane.

 

The bottom line is to use the lowest octane possible unless detonation in th engine is detected.

Most people do not realize that lower octane fuel actually has more energy or BTU. The "octane" rating is the ability of the fuel to resist detonation. Higher octane fuel actually has less BTU than lower octane fuel.

Since the Prius is not a high performance engine and uses the Atkinson (Thanks Tideland) cycle, the effective compression ratio is quite low. It is also not a high revving engine meaning 87 octane can be used which costs less money and theoretically should create more power and slightly higher effeciency.


Thanks!!

Brian
BT Tech
305-652-3115