Big increase in mpg since switching to ethanol-free gas

I’m not so much looking to field a discussion, but spitting this out because I’ve tested this for quite a while now. I know it’s not news, but I’m one more confirmation.

About 6,000 miles ago, I stopped running gas with ethanol in it. I’ve got a '96 Burb that was stuck at 10 mpg no matter what I did, how I drove it, etc. I switched to ethanol-free gas. First tank 12.6 mpg. Second tank 14 mpg. And it has remained at 14 mpg every tank since then, no matter how I’m driving it.

My grandpa once had this massive Cadillac, I believe the longest one they ever built. It had the same motor that was used in Sherman tanks if I remember correctly. A 500 cu in or so I believe. He used to say, “It burns five gallons an hour, whether it’s idling in the driveway or running 90 down the road.” I’ve owned a lot of vehicles with the Chevy 350 in them and I’ve always gotten about 15 mpg, and that didn’t really change much no matter how I drove them. That’s what they got in the 70s and that’s pretty much what they still get today.

I pay 5% more for eth-free gas, but get 40% better mileage. That’s a 35% net gain. 170 miles more per tank.

If your gas mileage stinks, I’d highly recommend switching to eth-free gas for a couple tanks and check your mileage for each tank.

I sit here scratching my head wondering how it’s better for anyone or anything if maybe I’m not the only one who was getting 40% less mpg by running fuel with ethanol in it. Require gas companies to add ethanol to the fuel, which reduces mileage (drastically in my case) while requiring auto makers to meet sharply increasing mpg standards. Something tells me auto makers run eth-free fuel when they test the mpg in prototypes.

None of this really matters. Just passing it along in case it helps someone else.

This seems to be a constant topic of discussion. I did some research a year or two ago on the energy difference between pure gasoline and E10 gasoline, and the energy difference between the fuels is on the order of one percent…

I don’t know what’s going on with your vehicle, but there’s no way that the E10 fuel your burning has 35% less energy than straight gas…heck, you could add 10% water to the gas, and your energy loss would only be 10%, not 35%.

I respectfully disagree with you, jesmed. I don’t discount your math, but gasoline and ethanol have different combustion characteristics. Plus, the ethanol-blended fuels also include EPA-mandated oxygenizers that also affect the burn rates. With the EPA-mandates, there are a lot of different formulations throughout the country. Here’s a map of different fuel requirements across the nation.

Couple all that with differences in engine designs and some react differently to these different formulations. I’ve heard lots of stories about noticeable mileage changes from winter fuels to summer fuels, and have no doubt that tthe OP noticed a big difference in fuel mileage from ethanol-blended, probably reformulated (RFG) gasoline to straight conventional gas.

I’m with busted knuckles. In motors, especially those with carbs, the associated loss of combustion due to the water separation can easily make a significant difference. Any sitting what so ever without the appropriate additives makes ethanol added gas less economical in practice. I think we feel that just adding water to gas means it automatically remains dispersed with out separation. The older a car, even with fuel injection, the less able IMO it is to deal with ethanol. At some point, even with the hypothetical 10% water, an older motor can be completely undriveable.

BustedKnuckles, you no doubt know more than I do about cars, so I defer to your superior automotive knowledge.

But I still have a hard time believing that the addition of 5 or 6% ethanol (which is roughly the % we get here in Boston) can result in such drastic losses. And I say that as a mechanical engineer with a minor in combustion who knows how to do the math and the chemistry. I could be wrong, but I wish someone would do a scientific study that shows such drastic losses, because I’ve never seen one…

And you raise a slightly different issue, the difference between winter and summer formulations. A while back I had a Tacoma that every so often had a significant drop in mpg that I couldn’t account for. That’s when I started looking into the summer vs winter formulations, and here in Boston I found that the % ethanol changes only a percentage or two between summer and winter…so the gas % goes from maybe 95% to 93%… which is even less significant an energy change…so theoretically, the loss of mpg due to seasonal variation in ethanol should be unnoticeable to the vast majority of drivers…I concluded that no way was the seasonal change in formulation responsible for my mpg loss mystery.

Since we’re on the subject, I dug up this study. it was done by the American Coalition for Ethanol, and of course they are trying to prove that ethanol is NOT an mpg killer, but after reading the report, I can’t find fault with their methods, though the sample size is limited, and they did not test older model vehicles.

Having said that, they found less than 2% loss of mpg, on average, with E10 vs pure gas, but because the E10 they tested was less expensive than pure gas, they found that, on a per dollar basis, the test vehicles averaged MORE miles per dollar on E10 than on pure gas.

Now, you can argue that the OP’s vehicle is older than the test vehicles in this study and may behave differently, but I sfill don’t see him losing 35% of mpg if these test vehicles are losing less than 2% of mpg on E10…

Oops, link to study is here:

I can’t speak to the math of the issue, but I just made a trip from northern Virginia to Flagstaff and deliberately sought out non-ethanol gas for the whole trip. My 2008 Camry normally gets about 32 MPG on the highway when driving this route, but this trip averaged about 35 MPG. This was not a scientifically controlled experiment, but the difference was consistent.

Although it’s common knowledge that this is true…
and as much as I’d love to buy such fuel…
it’s NOT common knowledge…

where the heck to buy the stuff ???

I immagine I’d have to pull into each and every gas station in town in hopes of finding some.
But do they really say so ? Can you really believe the lack of an ethenol label to indicate that it’s pure gas or are they just lazy about their labeling ?

And now that we know that, will the laws change so that we can save on fuel? I wish.

State by state listings of ethanol-free stations are at Generally the stations that don’t have ethanol make a point of stating it publicly.

I tried several tanks of ethanol free gas vs E-10 in my '88 Escort last summer, because I suspected the mileage would increase, but I was never able to tell any difference between the two. I’ve heard other people claim up to 10% increase in MPG on newer cars so thought it would be worth trying, but it didn’t seem to help on my particular engine (1.9L TBI with 4 speed manual transmission). A 10% increase would have been about an extra 4 MPG so even a 5% increase would have been noticeable and worth the extra money. Someday when I’m going on a trip in my '97 Escort wagon I may fill up with pure gas before leaving town to see whether I see any measurable difference or not. I also have a Scan Gauge in the '97 that’s been calibrated using 87 octane E-10 which would make testing a little easier. The price difference in pure gas and E-10 in my area is about $.05 per gallon or 1.5%. I do remember one time about 35 years ago when E-10 first became popular I was driving a '77 Buick Regal 350 CI 2BBL with automatic transmission on a highway trip from Toledo, Ohio to Elizabethtown, KY that I got about 21 MPG driving with c/c set at 80-85 MPH on the interstate, I never did know why the mileage increased on that one tank from an average of about 16-17 MPG highway to 21, but I’ve wondered if I had bought pure gas in Toledo when I left without even realizing it. I kept watching the fuel gauge and odometer and ended up driving between 50-75 miles extra on that tank than normal on the same trip and was pleasantly surprised when I checked the fuel mileage. That was the kind of mileage you’d have expected from a V6 of that vintage. That was the first time it ever got this mileage and was the last. I also know it wasn’t a difference in the fill level of the tank, because both times I had filled the tank to the cap and the mileage on the next tank didn’t come up at 12-13 MPG, but was back to it’s normal 16-17 MPG.

Math, chemistry, physics, or whatever might be the case, I specifically ran this fuel for the 6k miles in anticipation of people claiming that I drove it different to give it better mpg. Honestly, I can’t explain the why behind it. I’m just some anonymous nobody so I understand why it might be difficult to believe a 40% increase in mileage. But I’ve seen it myself. Tank after tank after tank.

Maybe it has more to do with the vintage of my Burb, though it’s fuel injected. Whatever the case, I’m still knocking down 170 miles more per tank with the eth-free gas, driving the same way I’ve always driven.

I’ve got an '89 Nissan pickup I’m going to do the same testing with, just to see if it responds similarly. Like my Burb, it’s an older fuel injected vehicle. I’ve already roped one of my neighbors into testing tank fulls with her Jeep.

Whatever the case, I’m done with ethanol so long as I have an alternative. Perhaps ethanol and its by-products are good for some vehicles, but my Burb seems to enjoy not having it in the tank.

I wonder if one way to generate some objective studies of it would be to remove the ethanol subsidies so that gas cut with eth shows its real price at the pump. If people saw it costed more than pure gas, I’d bet there would be quite a few people checking to see if the product is worth the extra money, just like they do with higher octane fuels.

In Mexico, the gasoline (both regular and premium) are 100% petroleum. I notice no difference in mileage (in a Crown Vic) when driving in Mexico or the States…A much more noticeable difference is observed if I’m driving with a headwind or a tailwind or traveling at over or under 70 MPH…

As I’ve said, I cannot discount the math. But math doesn’t explain everything. Alcohol just plain burns differently. I know from studies that the burn rate of alcohol versus gasoline is much slower, and alcohol has a higher octane rating. This could mean a difference in timing could be the reason for the MPG difference. I do know that the flex-fuel cars than can safely use E85 have sensors that detect the alcohol content of the fuel in the tank and adjust injector pulse and timing to best utilize that blend. I’ll bet that many newer cars are set up to run best on E10 or higher, and use the knock sensor to adjust timing to lower octanes, negating any noticable changes to MPG.

But, I know from practical experience that the many different designs sometimes leads to certain sensitivities to different conditions. I know Mitsubishi engines don’t run well with Bosch spark plugs. I know that Toyota’s don’t like aftermarket catalytic converters made by Borla. The math says all of these are made to specifications and should work just as fine as OEM, and for most cars, they do. But they don’t in all cases.

BTW, I have a degree in mechanical engineering, as well. I studied machine design and metallurgy. I worked as a mechanic when in school, and still turn wrench on the weekends, mainly as a hobby.

BurbBum, it sounds like you are getting the consistent, long-term mpg improvements you claim, so I will suspend my doubt and turn my attention to wondering why your engine seems not to like E10.

I do concede as BustedKnuckles has said that certain engines don’t “like” certain parts, or conditions. I do believe that, if we could get ypur Burb into a shop and run enough diagnostics on it, we could figure out why it runs so much worse on E10. I don’t believe it’s purely an energy deficit problem or a combustion problem. I do believe it could be something like a computer adjustment to E10 that’s causing it to run rich and impairing mileage…something like that.

But if people with 4 cyl engines can see only a minor, or no, loss from E10, there’s no reason a V8 can’t get the same result. So I do believe we could get the same results on your Burb if we could run the right tests and find out what the computer is doing differently between E10 and straight gas, or make the appropriate adjustments to spark advance, or whatever. Heck, speaking of engines not liking certain spark plugs, your E10 might burn better with a different type of plug. But without being able to run the tests, we’re just guessing.

My bottom line: the loss in mpg cannot be blamed solely on energy difference between the fuels, or on combustion physics. I believe there is something else going on with the engine, be it the computer or spark plugs or whatever, that’s not burning the E10 as efficiently as it could/should, and that with the right diagnostics and adjustments, The engine could be made to get your 13/14 mpg.

I’d say it depends on the car. I had a 92 Plymouth minivan the dropped from 18-20 on the road to 12-14 when I could only get gas with 10% ethanol. My other cars have gained less than 10% when avoiding ethanol.
It’s all academic for me now. Now gas without ethanol sold in my area, for that matter, no top tier gas either.

I noted that my well maintained 1973 Chevrolet Impala with a 350 V-8 2 bbl got 14 mph no matter where I drove it 100% city or 100% highway. Highway driving was on 2-lane state roads, rarely drove an interstate in those days.

Allow me to offer a theory.

Ethanol not only contains less energy than gasoline, but it burns slower. The most power can be gained at the top of the stroke, where the expansion caused by the combustion can increase the volume by the greatest proportion. As the piston moves down its stroke, the amount of expansion caused by a given amount of combustion becomes less of a percentage of the cylinder volume at that moment in time.

Said differently, it isn’t only the amount of energy in the fuel. It’s also where in the stroke it combusts, or, if you prefer, how rapidly and thus close to the top of the stroke it combusts.

In short, it doesn;t surprize me one bit to hear yet again that the increase in gas mileage gained by going to ethanol free gas is greater than just the difference in energy contained would suggest it should be. Makes perfect sense to me.

All of the commentary is interesting. I’m stating that seriously, not sarcastically. I have always enjoyed being around innovative people so it’s fun to read stuff from innovative people.

I have nothing to add to it, but I’m enjoying reading the comments.