Is there a recommended gas for Prius?

The Gen 3 Prius manual had a misprint calling for higher octane. It was later corrected. You can read about it in another earlier thread. The Gen 2 and Gen 3 both use 87 octane at sea level.

Tom

 

I also would be concerned that this info may be outdated, since 2004 gasoline and diesel is pretty much all ultra low sulfur.

 

OK, I'll give you that menno's rant was overly negative but:

You got confused on E85 vs E10. The title E85 boondoggle of the day was referring to E85, Menno was ranting about E10, you mentioned 15% which would be E15.

E0 = 100% gas
E5 = 95% gas + 5% ethanol
E10 = 90% gas + 10% ethanol (what menno was ranting about)
E15 = 85% gas + 15% ethanol (not mentioned in that article)
E85 = 15% gas + 85% ethanol (not mentioned by menno)

As long as you can't tell the difference between E15 and E85 you don't have a strong leg to stand on when complaining about his lack of intelligence.

The reason for the title mentioning E85 is because it's part of a long running series on TTAC about E85. It's assumed any discussion of ethanol laced fuel will get lumped under the E85 tag on TTAC because TTAC doesn't tag every article by the varying ethanol percentages.

Now if you had been reading TTAC for some time you would have seen Menno bragging about his two Priuses in thread after thread for some time. When 100% gas started disappearing in his area he noticed a drop in MPG. Sure he may be introducing inaccuracies to the percentage but:

(I wish I could remember where the article I read about this was so I could link to it but I'll go from memory and understanding rather than a link and quotes)

At least for the Gen II (2004-2009) Prius the computer can't be expected to adjust for fuel changes any quicker than a two tank average. Residual gas from prior fillups mix with the current fillup. If you do

87 octane
87 octane
87 octane
89 octane
87 octane

you won't notice much if any change but if you do

87 octane
87 octane
89 octane
89 octane
89 octane

you might notice a change on tank 2 or 3 of the 89 octane after the computer has tossed older data and the actual mix of fuel in the tank gets closer to what you last pumped.

Similar issues with going from E5 or E10 or E15 to E0. You need to drive on a new fuel for several tanks to give the car time to adjust to the new fuel.

Maybe the Gen III 2011+ Prius can adjust quicker but older cars don't adjust on the fly. Seems like I remember the article saying a car would average the fuel related data over the last 5 trips and that the average driver would refuel shortly after 5 trips worth.

Now the article didn't mention this concept but I'll toss it out there. Isn't it possible that even though the ethanol has only a few percent less energy in it, the engine computer could be running things based on prior fuel behavior and not be getting the best efficiency for the current fuel? Could that magnify the MPG loss of switching from 100% gas to E10 (90% gas/10% ethanol) at least for the first tank until operating parameters adjust to the new fuel?

As in maybe if Menno kept using E10 the MPG drop might not be as severe by the time he hit the 3rd tank?

Either way if he really did see a larger than 5% drop or just mismeasured a less than 5% drop. My choice for gas around here is something like $3.20 a gallon for E10 or $3.30 a gallon for E0. That's something like 3% price difference for something that may give me 3% to 5% difference in fuel efficiency and that's assuming the "E10" really has 10% ethanol. Some places have been found to spike the gas with extra ethanol. Getting 100% gas takes all the guessing out of "how much ethanol am I getting this time?".

And as to a cleaner atmosphere with ethanol. If the loss in MPG is linear as you say that still doesn't account for all the fuel used upstream to covert corn to ethanol. If you live east of the corn growing states you aren't getting cleaner air.

"Ethanol can't travel in pipelines along with gasoline, because it picks up excess water and impurities. As a result, ethanol needs to be transported by trucks, trains, or barges, which is more expensive and complicated than sending it down a pipeline."

If, and I do mean If, ethanol is energy net positive from field to my gas tank I'm all for it. If it is energy net neutral or net negative it needs to go away. And the biggest things that make it seem net negative are Corn Growers Subsidies and "Blenders' Credit" AKA Volumetric Ethanol Excise Tax Credit. That is Billions of dollars a year going to corn growers and ethanol producers.

But now we've delved into economics and politics. I think I'm saving money buying 100% gas, I think at about $0.10 a gallon more it's worth the price difference with gas floating in the $3 to $4 range. If you can't find 100% gas in your neck of the woods you don't have that option. If you do I'd suggest you find a time when the weather will be predictable for at least 4 tanks worth and try several tanks worth in a row of another fuel option and see how much you gain or lose switching to/from ethanol. Track the switchover tanks separately from the 2nd or 3rd tank of that fuel and see if there is a difference between the 1st following tanks. Switch back and see if you notice anything odd on the switchback tank vs the 2nd or 3rd tank after switching back.

 

there are way too many Menno posts to summarize here but I'll cover a few at least for your entertainment

July 16th 2008 E85 Boondoggle of the Day: E85 Is Cheaper Than Gas | The Truth About Cars Meno says "I can sum it up in one example. I very recently previously accidentally put 1/2 tank of E10 in my 2008 Toyota Prius. Got about 48 miles per gallon in mixed driving; pretty good, eh? The two 1/2 tank fill-ups after that, I made sure to put in pure gasoline (only one station in my town now sells pure gasoline and I have to go 10 miles out of my way to get it).

Just got back from that gas station where I put in 4.802 gallons again this morning. The computer indicated that I’d driven 301 miles since the prior top-up. I figure my ethanol percentage was probably in the 1% range or less.

For the mathematically challenged, that is 62.7 miles per gallon.

OK go back and read it again. 48 mpg on 5% ethanol solution, or 62.7 on virtually pure gasoline. That’s a 23.5% difference, folks."

Dec 9 2008 E85 DOA? E10 DOA? | The Truth About Cars Menno says "Besides I’m pissed off and fed up with 37 to 42 mpg on my Prius since E10 came to all our stations, instead of the 45-50 mpg i’d gotten used to on real gas."

Jan 9 2009 the first rant I linked to E85 Boondoggle of the Day: TTAC Prius Driver Says Ethanol Sucks | The Truth About Cars

Jan 23 2009 Menno Memo: Ethanol | The Truth About Cars a Pure Menno followup with a picture from Priuschat nonetheless. I'll let you follow the link for that one.

Feb 17th 2009 E85 Boondoggle of the Day: E20, E30 | The Truth About Cars

"Update on the Prius. Despite temps in the 20s and lower, with salty slush, ice and junk on the roads, snow tires on the car, etc. etc. – i.e. anything and everything to reduce the MPG of the car, I’m now showing over 45 mpg on the car computer. Because I’ve found real, 100% gasoline at ONE station in the area where I live, again. It is $2.09.9 per gallon, but paying 10% more and gaining 20-34% more MPG is obviously a good payoff for me.

You may recall my prior commentaries on TTAC – using E10 over the past few months (because I did not know about the last station standing with real gasoline) netted me 33 mpg on average in the Prius, rather than my 44 mpg “typical†winter average.

That means I was using 33.3% more fuel.

If you think I’m dense, don’t know what I’m talking about, think it’s “impossible†etc., please know these salient facts.

I’ve had two 2nd gen Prius cars; 71,000 miles combined between them over 4 1/2 years; I measure and compare the MPG on the computer; I have been measuring MPG since 1973 and have tested E10 in virtually everything I’ve driven since 1979 (back when it was called “gasoholâ€) and have found a 6% to 34% reduction in virtually every car I’ve driven/tested it in."

6% to 34% reduction in his testing for E10. Are his numbers right? I do not know, I don't think I'm wasting money paying 3-5% more for 100% gas though.

Unlike menno I usually gas up around the 2nd block on the fuel gauge and I don't bother to calculate gas mileage by hand. I'm happy when I see 60 MPG+ on the MFD.

 

I use any regular unleaded that is NOT from BP or any BP supported station.

 

I bet he consumes more gas going 10 miles each way to get gas than he saves using 'pure' gas.

 

Probably so.

I've gone 6 miles each way to get pure gas once but when I did I filled up the Prius and got a oversized gas can full for the lawn equipment while I was there. Used that gas all summer long mowing and weed eating.

Currently we go a few blocks to and a few blocks back from the gas station nearest the gym to get the 100% gas we put in our car on a regular basis. Probably costs us a mile extra each tank plus the extra cost per gallon.

I wouldn't suggest someone go out of their way on a regular basis for any kind of gas for a Prius or any other common car.

I would suggest taking advantage of a good gas station if you are getting 300 to 500 miles per tank and you regularly pas a station that sells 100% gas.

On summer gas I'm getting over 60 MPG on the ~16 mile commute and I figure I might be gaining or braking even on the 100% gas thing. I usually fill up if I see 100% gas any time I'm below half a tank but if I know I'll be by a station that sells it in the next three days I wait until 2 pips left so I won't have to fill up too often.

 

I had an experience that makes me think this is possible. I had been running shell gas exclusively and avg 4.5 - 4.8 l/100km. Then the closed a shell station near my work and there was an esso station across the street. So I filled up and on that drive home, and the next days commute I was wowed, I was getting 3.9 - 4.1. No major changes in my driving, no major outdoor temperature swings. However after about 150km it started to rise now it's about 4.2-4.4. I have a theory that the computer was running the engine lean beacuse it was expecting the other fuel but after a while it adapted to the new fuel and made the mixture richer.

However considering that the change took about 140km for my prius to show signs of adaptation I think it's very reasonable to look for changes tank to tank and not 3 in a row. If you reset the MFD 1/3 into the tank and record the other 2/3 seperately you'll probably get a more acurate reading.

I did some research on ethonol content law/regulation here in Ontario and found that the stations have to have a min avg of 5% for all the fuel they sell per year. Shell has 0% in their premium fuel and esso has max 10% in all their blends. They only have to post on the pump if the fuel may contain alcohol and what that max amount may be. So for shell to avg. out 5% on all the fuel they sell they must add more than 5% to their 87 octane. As far as I know all mid grade fuels are simply a mix of low and high grade done at the pump so I don't think the content of that grade needs to be considered. For Esso to meet the min avg they maybe useing less in the 87 and more in the 91 as the ethenol is a cheap octane booster. This is only a theory and is party based on my experience when I had a 1991 skyline gt-r that ran really poorly on esso premium and that was why I became loyal to shell and their 0% ethenol premium.

One possible way to do testing without having to wait to adapt is to unplug the 12v battery while there are open circuits (door open should be enough). This will cause the memory settings to reset. We use to use this technique at track days in my 04 Mini cooper S as the computer would reboot and very quickly learn the agressive driving of the track. On the drivehome it would take a while on the 3hr highway drive to watch the real time fuel economy gauge drop back down as the computer had to re adjust to cruizing.

I'm almost done my third tank with the esso and will be going back to shell for the next few. I will also try two premium shell 0% alcohol thanks just to see what happens.

Does anyone know if there is a chip or reprogram available to lean out the prius mixture and or advance ignition timing and take advantage of higher octane fuel. Is this even advisable in a modified Atkinson cycle engine? I did the same with noticible results in my 1.6l miata. That was simply a resistor on the MAF sensor and a rotation of the camshaft sensor that didn't re-map the settings at all but basicaly tricked the computer into starting the timing 10 degrees early and having a little bit more air than it actually knew about.

 

"The North American Prius uses a rubber bladder system. However, the rubber is temperature sensitive and will shrink/stiffen in cooler weather lowering the tank capacity from the default 11.9 gallons.

"Slow filling of the tank with careful "burping" of the fuel inlet past the first "click-off", without spilling, will stretch the bladder back out and restore the original tank capacity."

"The tank is 45L (11.9 gal., 9.9 Imp.gal) and decreases by 5L (1.3 gal., 1.1 Imp.gal) @ -10°C/14°F."

I'm not going to shrink the bladder on my Gen II just to run the tank dry when switching fuels. My normal fillup patterns will mean mixed fuel for at least 2 fillups after a switch.

If I fill up at 2 pips/blocks maybe I'm putting in 8 gallons out of 12. Whatever the fillup is lets assume I do it when 1/4 of the tank capacity remains. So if the prior tank is E10 and the current fillup was 100% gas the new mixture still has 2.5% ethanol aka 97.5% gas.

The tank after that (again assuming 75% new gas to fill up a tank) takes us to 0.625% ethanol or said another way 99.375% gas. Close but still enough ethanol to possibly effect the way the engine computer does things.

The next tank takes us to 0.15% ethanol. I'm going to assume that 99.85% gas is close enough to 100% gas that the engine computer won't notice the difference.

If not then tank 4 gets us to 99.94% gas (starting from 90% gas and blending with 100% gas at 1/4 tank left before filling up, and doing so 4 times).

Yes you'll see a difference each tank but you aren't to 100% gas on "tank 1" or "tank 2" after "switching" to 100% gas. It might take more than that, I honestly don't know how well fuel mixes in the bladder of a Gen II Prius. I'm assuming vibration and acceleration in multiple planes will be enough to thoroughly mix the fuel during the 300+ miles before I fill up again.

 

Thanks for the clarification. The title is what confused me. The title stated E85, then he wrote about E10. So actually, even though I knew the difference, I figured he was the one that was confused. Also, be careful on your choice of words. Not knowing the difference between E15 and E85, is not a lack of INTELLIGENCE. It's actually a lack of KNOWLEDGE.

Either way, the gist of my rant was based on losing 35% fuel mileage using 90% gasoline and 10% ethanol. And basing that 35% loss on a very small sample size. But I really enjoyed reading your post.

Also you had a very interesting thought whether it takes a few tankfuls to adjust to the E10. I am not certain about the Prius, but on my other car, it runs closed loop control on the O2 sensor unless it's at WOT. At WOT it goes open loop and then it looks at history of the fuel trims to decide what fuel to give the engine. But in normal part throttle operation, the engine just operates close loop to the O2 sensor and adds or subtracts fuel based on exhaust gas readings. I would think the Prius engine does the same.

Thanks,
Glenn

 

The Prius is like most vehicles. It runs open loop at warm up then goes to closed loop. Depending on load, power demand and other factors it may switch back yo open loop. I've observed this even while just cruising.

 

On my first tank of 100% gas (vs the approx 5% mix of regular) I saw a noticable improvment and have got a new low record of 3.4 l/100 over a 63km period. The only 100% gas available around here is the premium 91 octane unfortunetly. So far the tank is averaging 3.8l/100 km (MFD) vs my previous tank best of 4.4 (MFD - 4.39 calculated). I haven't filled up yet to calculate it but most of my tanks come out to less than .1 l/100 acurate.