Premium Gas and MPG

It will make a small difference.

But in terms of $ per mile, not worth it.

Maybe while you are at, avoid ethanol.

 

All ethanol free gas that have found is Premium (higher that 87 octane). That might be the reason, not higher octane, but zero ethanol, which is lower in energy density that gasoline.

 

I drag race low powered cars and always check my mpg. My 95 Neon has the base SOHC motor and the only mods are lighter wt, TB from an automatic car (mine is a 5 speed), elimination of power steering, and better flowing exhaust with stock header. On a few occasions I have used premium and on every time it got slightly worse mpg and also ran slower in the qtr. My 84 Horizon has a 2.5 motor converted to a carb, header, cam, and about 12 to one compression. The computer has been disconnected since the diaphram fails at the most inopertune time and costs me races, so I only use it to start the car...base timing only of 10 degrees. Without timing advance it starts running more inconsistant when shifting past 4750, so I shift there...bracket racing needs consistancy. I used to use regular fuel until the mods that have been mentioned. When I now use premium it still runs no quicker and the mpg is a tiny bit worse. I have never tried premium in my Prius, and never will. On all my previous cars that have not been modified I had the same results as far as mpg and performance. If I ever had some spare change I would love to get a old Horizon and gut it like mine (1890 lbs currently and STILL driven to every event) and mate it up to a Prius drivetrain! When the Horizon was still 1890 lbs and had a stock 2.5 except for carb it would run 16.7s in the qtr mile at only 77 mph....the Prius ran 17.7s at 80! My 60 foot time in the Horizon used to be in the 2.2 second range, now nearly 2.0s...the P is about 4 tenths slower.

 

Octane is not energy content, they are independent variables. Higher energy content will give you better MPG, but nothing on the pump will specify energy content.

As an example E10 gas will have higher octane and lower energy content (by 3%) than the same gas with no ethanol. typically it will cost more than 3% more than E10, so you lose money getting better MPG.

E85 (which Toyota warns you against) would have 30% less energy than E0, so is only economical, even in a car designed for it, if it costs 30% less. (and your time pumping gas is free time)

 

Never noticed a difference in MPG. Only wallet

 

Higher octane gas burns slower, so unless you have a knock sensor that advances timing to take advantage of premium you won't see any mileage benefits.

 

My gasoline testing revealed a maximum hill climb, premium would make a slight difference. But the higher energy content was found in only a few of the 89 octane gasoline samples. Since E10 is not a hard ratio and difficult to even field test the ratio, I don't test it.

Bob Wilson

 

Just wait till you see how they add ethyl alcohol. I watch from our amateur radio club site as the fuel tankers, "about" 90% full, wheel into the ethyl alcohol plant, and are topped up with alcohol. Very precise, right?

 

Yes hypermilers might like Premium as well as E0, especially E0 and Premium combo.
As Jimbo mentioned, the energy content impacts MPG.

However, in Reformulated Gasoline areas (like CA, MA, NoVA, NJ etc), which I figure is at least 50% of Prius drivers, Premium is not expected to have better energy content. Also E0 is essentially banned in those areas as well.

So if you live in CA, or MA, don't bet your monthly paycheck on winning the Gen4 per tank distance contest.

Here's a map of gaso blends...although as a simplification we can say all gaso is equal, obviously it is not exactly equal if we can have a map like this.
http://www.nacsonline.com/YourBusiness/FuelsCenter/Documents/2016/US-Gasoline-Requirements-Map.pdf

 

Chevron's highest grade, in my area anyway, says it's ethanol free. All the other grades say something like "may contain up to 10% ethanol".

I've never bothered to try other grades, believe it's only necessary to prevent pre-ignition in higher compression engines, and would be spec'd in the owner's manual.

 

Separate from E0-E10 and RFG issues, the Premium vs Regular impact varies with blending specifics that are not normally disclosed to the consumers.

When my sister (now retired) was blending fuels at a local refinery early in her career, she indicated that the premium octane gasoline from her plant generally had slightly lower energy content than the regular octane, therefore should produce slightly lower MPG. But with numerous different regional and seasonal blends, and different batches made from different available component stocks and reprocessing, there was no single or simple answer to this question.

EPA and other requirements have changed significantly since then, so I have no idea what the current situation is, other than it should no simpler now than then.

 

All of which underscores the fact that gasoline is not a single chemical compound, it is a variable mix of various compounds in varying amounts. Unlike say ethanol, propanol, or methanol, each of which is a single compound. Purifying gasoline to a defined mixture would be too expensive, and is unnecessary for its purpose anyway.

Maybe I'm wrong, but I read somewhere that gasoline is shipped as a base stock and that different chemical packages are added to it when it is delivered to the station to boost the octane to premium, regular, etc. I thought that this explained why the price differential between premium and regular ($0.20? per gallon) remained constant even as gas prices shot up: the difference in cost of the various packages had not changed. Is this true?

 

Here in Edmonton I watch the fuel tankers filled to the 90% mark pull into the ethyl alcohol plant to "top up".

Many Mohawk stations (same as Husky) use "blending pumps". They have two grades of fuel, "super premium" with octane rating of 94 I think, and "regular", with octane rating of 87. All have ethyl alcohol added. When you buy intermediate grades the pump blends the two listed above to achieve the other octane ratings (90 and 92, as I recall).

Still more complexity!

 

Aside from ethanol which has high octane, there is really no legal additive to boost octane. Metal additives like tetraethyl lead and MMT will do the trick, but are not allowed at least in the USA. So Premium needs to be refined harder, and really quite harder to make with EPA mandates. Especially reformulated gasoline premium (CT, CA, VA etc) is harder. There are detergent additives added.

Fortunately as Prius drivers we don't need the Premium. I rarely it use it but maybe in the mountains I'd give it a try to help my aging HV batt get up the hills. If I lived in a non-RFG area, Premium might be of interest to me to boost MPG a little, but I do not live there, so Premium is a lost cause for me.

 

Prius engine has a compression ratio of 8:1. Therefore, there is nothing to be gained by using premium (91 aki / 95 ron octane). Keep in mind that, you cannot buy cheap regular unleaded (87 aki/ 91 ron) in most states of Europe, not even in Greece where there is supposed to be a "financial crisis", due to German auto manufacturer interests. But Prii in Europe get worse mpg than in US. Also I found some quite interesting answers to the question Is high-octane premium gas more costly or difficult to produce compared to regular unleaded?

Why is gas more expensive the higher the octane grade? - Quora

These guys claim there is a significant environmental footprint when it comes to refining crude oil to premium gasoline compared to regular.

 

Not on the tests. "Typically, there's a 20 to 25 percent difference between European NEDC and U.S. EPA fuel economy figures: A new Toyota Prius is rated at 60 mpg in Europe, exactly 20 percent more than its EPA combined rating of 50 mpg." - Why European Gas-Mileage Ratings Are So High--And Often Wrong

 

I would expect better Prius MPG in UK/EU if we're talking about fuel differences alone. Basically better energy content without the EPA mandates we have, including E10.

 

OK, so I'm perplexed. If it's harder to refine gas to premium than to regular, how come the price differential her in CT remained the same, I think it was $0.20/gallon?, as gas prices rose from $2-ish to >$4? To the point where I thought "why not get premium?" I would have expected the differential to be a percentage of the per gallon price.

 

do not know because pricing policy is proprietary secret. I am surprised though, here Premium was much higher price when prices were higher. Keep in mind the cost to refine, though a massive effort from a scientific/engineering perspective, is a relatively minor cost component compared to crude oil cost and taxes etc.

Therefore Premium is probably priced more to control supply and demand rather than recover exact refining cost per se. In particular EPA gaso. recipe regs largely prevent USA oil cos. from playing their old games of hyping Premium formulations (so hard to make now), so oil cos. would probably rather sell you Regular. Perhaps now with cheaper crude prices, oil cos. have more incentive to sell Premium due to the better profit margin on Premium, so maybe they are willing to make the cost differential less to move more Premium. My guess-planation I am engineer not a marketer.

PS- But even if Premium is only 10 cents more I ain't buying it in CA, North Va. or CT because EPA RFG Premium has no energy content advantage (according to a Chevron website discussion).