Ethanol’s an interesting fuel. Blended with gasoline, it can offer big octane and serious knock resistance, but it can also wreak havoc on incompatible fuel systems. While a 10 percent blend has been fairly normal at the pumps for decades now, E15 looks like it’s sticking around, and while it might be tempting to save a little bit on fuel, there are some reasons why it isn’t ubiquitous yet.
This cheaper blend with an extra slug of distilled corn juice has already been around for a while, but it’s historically been isolated to use in cold seasons, when smog is less of an issue. Over the past few years, a number of emergency orders have extended the sale of E15 through the summer months, and it looks like that’s continuing for 2025. However, just because it’s available doesn’t mean you should just put it in your car.
The EPA claims that cars made after 2001 will happily accommodate E15, but that’s not exactly accurate. While E85-capable vehicles can safely handle E15 since 15 percent ethanol by volume is far less than 85 percent ethanol by volume, there are lots of vehicles made after 2001 that aren’t designed for E15. For instance, BMWs only approves a maximum of 10 percent ethanol content in its vehicles, as does Mazda, as does Mercedes-Benz on all models not approved for E85. Volvo only approves a maximum of 10 percent ethanol content across its lineup, as does Mitsubishi.
Some other manufacturers like Nissan are more selective when it comes to E15 approval. The current Frontier, Rogue, Z, Pathfinder, and Altima can take E15, but the Sentra, Kicks, and almost all outgoing models like the previous-generation Armada aren’t rated to handle it.
So what happens if you run a car not rated for E15 on this particular blend of gasoline? Well, ethanol is hygroscopic, meaning it pulls in moisture. If not kept tightly sealed, the ethanol in blended gasoline can attract water and separate from the gasoline, potentially leading to fuel system damage. Thankfully, modern fuel systems are generally sealed pretty well, but water contamination isn’t the only way higher ethanol concentrations can affect fuel systems.
For instance, ethanol and oxygen can form acetic acid, the active ingredient in vinegar. Anyone who’s let old parts sit in a vinegar bath overnight will tell you it does a modest job of removing light rust and tarnishing, but similar acidity could also affect the integrity of fuel system components over the long run. It’s also worth noting that rubber fuel system components are rated for a certain level of ethanol, and lines and seals compatible with E10 might not be compatible with E15, leading to premature degradation.
Another thing to note about E15 is energy density. According to the Department of Energy, pure ethanol is roughly 30 percent less energy-dense than gasoline, so going up from E10 to E15 will likely result in a marginal decline in fuel economy. It will likely only be a few percentage points, but if the price of E15 in your area is only a touch cheaper than E10, you might not actually save any money.
Yes, E15 will likely be cheaper than more common blends of up to 10 percent ethanol, but it’s a good idea to check your owner’s manual to see if your car can run it before selecting it at the fuel pump. One mistaken tank probably won’t do any damage, but prolonged use in a fuel system not designed for it could result in unexpected wear. Also, reduced energy density means E15 might not work out cheaper on a cost-per-mile basis.
Top graphic images: stock.adobe.com; Nissan
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But e15 is the perfect solution to filling up the gas tank in a rental before you return it.
I have been reading up on nitropropane and other fuel mixtures, and they make a point of reminding everyone that not all octane fuels carry the same power output, particularly regarding low rpm torque.
Ethanol can be especially deceptive unless you tune for it specifically.
Ethanol is why I changed to diesel.
No regrets.
Real petrol is much more expensive here, as it is shipped in.
Something that seems to be left out of the comment section here: Ethanol is great race gas. My 89 Foxbody with a 545ci big block makes 700/700 on E85. The only alternatives for fuel would be leaded race gas or other super expensive race fuels due to the high compression.
If you have a turbo or supercharged car 15% ethanol has significantly higher knock resistance than 87 allowing you to make more boost with tuning or have less detonation. For the hypermilers, it also means you can downsize the engine or increase compression without significant issue.
Been running up to E30 in a 2007 BMW F800S motorcycle for 18 years now, turns out it was built to run on Brazilian E25 right from the factory!
So the big tak-away is if you use E15 then use it in a daily driver not a weekender car.
Also don’t use E15 in lawn equipment it’ll tear those hoses apart or you will have water issues.
I accidently put E15 in my push mower and it wouldn’t even turn over. After draining it and adding some (very expensive) E0 gasoline, it turned over immediately. I don’t mind it in my car because I do well over 450 miles a week but I definitely wouldn’t let it sit anywhere
It should be sold at different pumps, like diesel is. I’m sure a lot of people accidentally put it in having no idea that it’s bad for their vehicle.
In Ohio they have special blue pumps and get their own price and disclaimer
My kid told me that also in Ohio they have skibidi toilet rizzlers…
I just asked my 10 year old daughter about those last three words and she just sighed and shook her head.
10yr old on this end too, the lingo is funny AF
As the mom of an 8-year-old, this cracked me up.
Out my way they are different pumps. Diesel pumps are green, E85 is yellow, E15 is blue, and everything else is “eh, whatever”.
There’s a station near me that sells all of E85, E15, E10, E0, and Diesel. I’ve definitely circled the pumps in confusion looking for the fuel I want. I suspect a lot of people don’t know, don’t care, and just put whatever in. If they discriminate at all it’s just to select the cheapest option.
My old Focus said on the gas gap not to use any concentration higher than E20. I put E15 in it several times on highway trips just as an experiment. I swear the Duratec 2.0 would run on any swill you put in it- and couldn’t tell the difference. For the 100k miles I had it for I usually filled up at the cheapest place around, which was also conveniently the closest station to my place. Different brands, different octane, never made any difference in performance or mileage. Never knocked, never failed to start.
I had a 2015 Focus company car for a while that was flex-fuel rated (up to e85). Same n/a 2.0 four popper. Higher ethanol blends beyond the standard 10% are relatively rare in Texas, but a few times I tried e85 in it just for the hell of it. It consistently lost about 10mpg, and if there was any performance benefit, it was imperceptible.
being that car on normal e10 would do about 40mpg on the highway, it was losing 25% of it’s fuel economy, but e85 was only about 15% cheaper than regular gas, so it was solidly a losing proposition value wise.
but it gets votes in Iowa…
I am brought to mind of a Scotty Kilmer short where he measured the ethanol level of a tank of gas and found 22% ethanol. Does anyone know the tolerances allowed?
https://www.youtube.com/shorts/0DBNG7RjCjY
given the source I’d immediately be suspicious of the methodology
I just want to know who is measuring the amounts and if it is true.
Ethanol is a GOP subsidizing for farmers. Kind of surprised it wasn’t killed off by DOGE. Uh, wait…..China subsidizes stuff…wait, only bad if “they do it”. Don’t want to disturb the base
Don’t blame it ENTIRELY on the Republicans. Ethanol subsidizes have been a way to court the Corn Belt vote through many administrations. As a resident of that area, I personally thing its dumb to waste farm ground growing motor fuel.
I grew up in that era when that was enacted. It was somewhat bipartisan at the time, but they are red states. M K and I went over it above, and indeed, corn growing is not the best use
Every time I pay more for groceries, I am reminded of the ethanol scam.
So, every day, every time I eat.