Five Things You May Not Know About Flex-Fuel Engines

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Five facts about flex fuel engines

1. They’re pretty much the same as a normal engines. Aside from a different set of spark plugs, injectors that can pulse more fuel, and a more corrosion resistant fuel system, flex-fuel engines are essentially identical to regular old gasoline engines. To see what “essentially” means, read more below.

2. When you run E85, your fuel economy drops 20-30%. This is because ethanol contains less chemical energy than gasoline. Put another way, ethanol burns cooler than gas, so it takes more than one gallon of ethanol to do the same amount of traveling that you can do on one gallon of gas. Provided that E-85 is at least 20-30% cheaper than gas, it’s a push. Otherwise, running E-85 might be costing you money.

3. E-85 absorbs water like crazy. That’s not a scientific observation of course, but it’s a good description. Check this out:

ethanol is hygroscopic by nature. This means that it immediately soaks up water both in liquid form and as condensation right from the atmosphere. Hence ethanol cannot be transported through petrol pipelines. Worse yet is that any prolonged exposure to the air itself can begin to dilute ethanol (due to water absorption)

This explanation from the Energy Refuge blog is specifically about the transportation problems associated with pure ethanol, but all of the above information applies to E-85 fuel.

E-85 will absorb whatever water is nearby, and given enough time it will dilute itself enough to cause combustion problems. While is is very rare, it *is* technically possible. The downside to water absorption is that burning “wet” E-85 can cause excessive amounts of formic acid to be created during combustion. Formic acid can eat engines, which means that…

4. A flex fuel engine’s parts are treated to resist formic acid. Because the risk of water contamination in an E-85 engine are fairly high, automakers use a special nitride coating on all the internal engine parts that may be exposed. This prevents excessive wear if a particularly watery batch of E85 is burned.

5. Manufacturers may recommend more frequent oil changes when running E-85. If you live in an area where E-85 is readily available and cost effective, you may be using it every day. If so, your local dealership may suggest you change your oil more frequently. Their reason? Acids formed during ethanol combustion can reduce the lubrication properties of motor oil, therefore requiring more frequent changes.

Unfortunately, this is pure hogwash. Most modern oils contain more than enough detergents to nuetralize the acids that E-85 may produce without compromising lubrication, so they do not need to be changed any earlier than normal. Read more about why more frequent oil changes are not needed if you’re running E-85 if you’d like to find out more.

6. (Bonus!) When your manufacturer built your flex-fuel vehicle, they got a special fuel economy credit from the government. In a system that’s both unseemly and absurd, auto manufacturers are given fuel economy “credits” for building flex-fuel vehicles even though these vehicles don’t get better fuel economy. The TerraPass blog has a great post that explains how a Chevy Suburban was credited with a 30mpg fuel economy rating despite actually getting 12-16 mpg – check it out.

Finally, for you Tundra owners out there, a flex-fuel engine is not compatible with the TRD Supercharger.

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  1. mk says:

    #5 and #6 I didn’t know. For #5 then, why do mfgs. state to change oil at 2500 miles if use over 50% of the time E85? You would think the car mfgs. would know what they are talking about don’t you think? #6 is a crock of hogwash. Fuel credits to build E85 vehicles when in fact E85 reduces fuel economy by around 25%. This seems to contradict saving fuel don’t you think even though not pure gas or even E10 gas. Unless I am strapped for cash or over 25% cheaper E85 vs. E10, I will never buy E85 since I lose 25% fuel economy from say 13.5 from 17 mpg running E10. Lately here in the midwest, E85 has been only 22% cheaper so it is not worth using. But, a few years ago, E85 was over 30% cheaper and then it pays to use it more often, but never over 50% of the time since I still don’t trust the internal parts of the engine to handle the E85 stuff.

  2. Mickey says:

    The problem now is finding a pump that doesn’t have E-85. Dang near everyone has it now. You’re stuck with that fuel.

  3. Danny says:

    my 2010 d/c is not marked as flex fuel. also, i’ve never seen a e-85 pump im mississippi or tennessee. so, if i’m in an area that only has e-85, can i still use it temporarily until i find normal gas or e-10?
    i also think it’s stupid to use a food source to make an inefficient fuel. switch grass is a better candidate for this but there’s no money to be made growing a weed. when corn prices shot through the roof due to higher demand caused by ethanol mandates, our food prices went up. corn is used to make dog food, catfish feed, hog feed, cattle feed, chicken feed, human food, etc, etc. all of these went up due to the corn being allocated to fuel production. economics 101; the greater the demand equals a greater price, as long as supply is limited. also with more corn acreage being allocated, there is less acreage for other foods to be grown.

  4. Danny says:

    also, there are a few gas stations here that market themselves as carring “pure” gasoline. they are about 10 cents a gallon higher but well worth it compared to e-10.
    also, ethanol will kill you weed wackers, chainsaws and lawn mowers. when i cant get pure gasoline, i run a little seafoam in the fuel as suggested by napa and autozone. i also heard that stabil is strongly suggested. i’m not sure how true this is, but i’d rather not risk my gas powered tools. also, my old 1995 z-71 ran fine until she had to run ethanol. i cant prove it, but it seems very coincidental.

  5. TC8 says:

    There’s probably no reason to mention this, but E85 is an excellent race fuel (about 105-110 octane rating)as well as burning cooler than gasoline. I use it in my 06 Mitsubishi EVO and 03 Mustang Cobra with excellent results. Because E85 burns cooler and has a higher octane rating than gas i am able to run with higher boost on both vehicles. Fuel economy does suffer a bit (anywhere from 20-30%) so I had to upgrade to higher flowing fuel injectors and fuel pump to compensate for the extra flow that was needed. E85 is also about 20% cheaper at the pump then regular gasoline, not to mention race fuel. With that said i wouldn’t use it on a daily driven vehicle because of the fuel mileage issue.

  6. mk says:

    E85 might be higher octane, but with 2 somewhat expensive racing type cars, why would you risk ruining your engine using E85 TC8? E85 agree or even E10 is not good for smaller engines like outboards, lawnmowers, roto-tillers, weed whackers, etc. and try to buy 93 octane no ethanol pure 100% gas, although paying a premium at about 30 cents more per gallon, but besides the lawnmowers, I do not use those small engines that frequently, so I pay the increase to hopefully make the smaller engines run better and last longer. Although, I begin to wonder how long the 100% 93 octane gas is sitting in the holding tanks at the gas stations since not too many people use that type of gas thus creating stale/possibly watered down bad gas as well. I also use seafoam and/or mystery marvel oil which seems to help, so far, good luck no problems in the gas tanks.

  7. TC8 says:

    I would never convert my 08 Tundra to run E85 as fuel economy will suffer, especially as it’s my daily driver, but as a race fuel for my other vehicles i really don’t see a downside beside more fill-ups when i do drive them. The first few oil changes after converting to E85 i had the motor oil tested and found no issues running E85 so i’m currently back to 5000 mile service intervals using synthetic oil. There’s really no issues with water absorbtion as fuel tanks are sealed fairly well and the fuel will never sit long enough anyway. The reason vehicles break down when running on E85 has nothing to do with the fuel itself, but the amount of fuel needed to properly feed the engine. Keep in mind E85 doesn’t have the combustion energy that gas does, so it will take more E85 to create the same energy. If you don’t increase the fuel pump and fuel injectors accordingly along with a device (or reflashing the ecu) to drive them the engine will lean out which will cause detonation, and that’s what kills engines. My 2 cents.

  8. Jason says:

    mk – To your first point, I agree. Don’t see how there’s a government fuel economy credit for this system. I also haven’t seen E85 at a price point that made economic sense…but some companies use it because the net carbon placed in the environment is much lower (practically zero).

    Mickey – Interesting. I see lots of 85 octane, but E85 is sort of rare in my neck of the woods.

    Danny – I’m with you all the way on the economics of corn. Brazil makes ethanol with sugar cane, and while that’s not really economic either, it’s better than corn. As I’m sure you know, the holy grail of ethanol production is to use “cellulosic feedstocks” – things like corn husks and grass clippings – to make E85. There is some interesting research going on related to termites:

    Maybe someday we’ll make our own gasoline alternative using some sort of termite based fuel machine…LOL. It’s exciting to think about being petrol free (or at least much less dependent).

    As for your question, you probably could get away with running a few gallons of E85 in a regular engine without any long-term damage, but I wouldn’t risk it. Better to pay for a tow bill or rental car…a watery batch of E85 could destroy your fuel system. That my explain why E10 ruins lawn tools that are likley to accumulate moisture as they sit unused for days or weeks at a time.

    TC8 – It’s funny you say that, because the racing uses almost made the list! Great point. When an engine is designed/tuned for E85, the compression ratio can be much higher, efficiency can be better, etc. It’s much cheaper than racing fuel too…and I wouldn’t have thought of that one. Great comment!

    mk – I think TC8’s response to your second comment is correct – the risk to vehicles is low. However, for small gas powered motors not designed for gas/ethanol mixtures, the risk is higher…especially because they sit so long between uses. That’s a formula for absorbing water I think.

  9. texmln says:

    You say an e85 engine needs different spark plugs to pulse more fuel… don’t you mean different fuel injectors? Every modern E85 engine I am aware of has fuel injectors with a much wider range of fuel delivery since they may need to pump out almost twice as much E85 vs. gasoline in similar instances.

  10. Jason says:

    texmln – Aargh! Typo!! 🙂 Thanks for catching it – I adjusted the article.

    That’s what I get for writing posts at 11pm!

  11. TXTee says:

    So what’s the real benefit of running E85 in a Tundra, especially if you live in a region that doesn’t offer it? I may have missed that part when I browsed the article.

  12. Jason says:

    TXTee – I think that there are some places where E-85 is financially attractive, and of course that will change if oil prices head back up.

    The other reason that E85 is purchased is that it reduces a company’s carbon footprint. Some companies use E85 exclusively in their fleet vehicles to make an environmental statement.

  13. TXTee says:

    Hmmm so the consumer ends up paying for the E85 image. LOL…got your points, Jason. Thanks as always. Glad to see the articles are still here. Was the feed notification not working?

  14. Jason says:

    TXTee – Not sure – are you saying that you weren’t getting any RSS notices?

  15. TXTee says:

    Something like that….I didn’t see the posts on the forum page’s left side link and assumed there was nothing new. We also keep the RSS feed on the GCT site to notify members when there’s a new article…..and they all came flooding in one day.

  16. Jason says:

    TXTee – No idea…could be the GCT RSS feed, could be something I’ve done, could be a random error. Hopefully it’s fixed now!

  17. Jon says:

    Hi, I just purchased a FF Tundra. I had thoughts of putting a SC on it until I just found out it is incompatible with the FF 5.7. Is this true and is there anything I can do to make it possible to install a SC. thanks,

  18. Jason says:

    Jon – Sorry to say it, but no. See the comments on this post for more info:

  19. MJM says:

    have ran many different vehicles on E-85 for about 15 years and absolutely love it fo the following reasons;

    1. It is 100% American Made so I am doing my part to stop the transfer of wealth to the Middle East. We import 1 billion dollars of crude oil per day and much of it is from hostile reagions of the world.
    2. Much cleaner than gasoline.
    3. It is renewable

    Also, If you are most concerned about the mileage, I often blend it at 30% ethanol 70% gasoline and get very minimal mileage loss and I have found it to actually be less cost per mile than E-10.

    • liveload says:

      It is apparent that not many people understand how the modern commodities markets work. Fewer still understand how that ties into US Foreign Policy. Do the people who understand these things a favor and educate yourself. The same hackneyed old tropes, tailor made left/right/center talking points, get trotted out decade after decade and it’s doing us no good as a society.

      The reason some people feel that nothing makes sense in energy and foreign policy is because they aren’t working with the facts.

  20. Firstseeker says:

    Hi all, i want to buy a 2011 or 2012 NON-FLEX FUEL Toyota Crewmax 4×4 but i can’t seem to find it. All the dealers are claiming it does not exist. I can find it on the Toyota page and on the Edmunds page, but everyone is claiming Toyota only makes Flexfuel crewmax 4×4 now. any ideas?

    if not, can you suggest an alternate vehicle?

  21. Jason (Admin) says:

    Firstseeker – You can buy a non-flex fuel Tundra, but you have to look in a different region. My suggestion? Check with a Toyota dealer in Phoenix or Dallas. In years past, people could buy non-flex fuel Tundras in those markets.

  22. gerard Jonkman says:

    Hello All,
    Im a toyota driver in holland and have problems with my Tundra flexfuel 5.7 flexfuel 2012 , the problem is that we having start problems,the Car gives in his history (OBD) 86% ethanol and we never use that in holland, but the car needs to be reset every month because when its reset the percentage is 0 % and no problems,after 1 month 86% and no starting anymore, nobody can help me here so perhaps anybody can give me some answers,we dont get support from Toyota USA because this are side import cars.
    The locall dealers dont know this cars and we cant find a sensor Please who can help me,
    regards gerard jonkman

    • Wow, you have a Tundra in Holland. Send some pics.

      As to the other issue, I’ll send it around and see what we can find out.


      • Gerard,

        Here is what I got: My advice to him would be to record the codes being set by the computer, then email them to a Toyota dealer who is willing to provide help.

        Hope that helps.


  23. BriBri says:

    Doesn’t sound like flex-fuel offers any practical benefits over regular gasoline. But I guess the government’s propensity to kowtow to the eco-terrorists isn’t rooted in any kind rationale thought process.

    At least it keeps corn-growing farmers in business. 🙂

    • BriBri,

      The benefit is using less oil and less dependence on fossil fuels. That’s about it.


      • BriBri says:

        What is the (realistic) benefit of using less oil? Why should we be less-dependent on fossil (petroleum-based) fuels?

        If the gummint let us drill into the vast petroleum deposits within our own continent, the economic benefits would be greater than relying on foreign oil. Also, it has been proven that gas-diesel is a more efficient (from a cost-benefit perspective) fuel over the long-term.

        Bio-fuels have a long way to go to prove themselves before the masses will be swayed away from ‘gas-guzzlers’.

        • BriBri,

          I’m a little taken aback by your statement of why we would want to be less-dependent on fossil fuels. I, frankly, didn’t think there was a pro-oil argument still out there. Even the oil companies like Exxon realize that oil drilling is not a long term solution. To be blunt, we will run out of oil sometime in the future. What we do when that happens largely depends on the decisions made today.

          I find it interesting you don’t think we are drilling enough. The latest facts and news stories point to a large increase in domestic drilling and in fact, the US became a net exporter of oil in 2012 (

          Oh and if that link is too liberal for you, here is a Fox News link. – Story says, “And U.S. oil production, at more than 7 million barrels a day, is at the highest level since the late 1990s.”

          It has become clear that drilling more oil has NOT resulted in lower gas prices. It has resulted in less dependency of foreign oil imports. The reality is that the world is using more oil/gasoline and that increase is affecting the global market. If American’s want lower gas prices, new car technology with MPG savings is a big part of the solution.

          Yes, bio-fuels have a checked history. Agreed. Yet, they have to be part of the equation. With fuel economy up, fuel consumption is also up according to a University of Michigan study. If there is a bio-fuels or alternative fuel that would drop consumption, we would all see a real benefit in fuel prices. And yes, the study does point out that mileage driven plus load weight has a real impact as well. We have chronicled in the past on this site how the more you weigh, the worse fuel economy you have. That’s a fact.

          Whether you agree with the above or disagree, it seems the facts are becoming more drilling doesn’t lower gas prices. Americans are dumping gas guzzlers and buying more fuel efficient cars.

          My two cents. 🙂


          • BriBri says:

            I hear you, Tim. I’ll see your two cents and raise you two cents…

            I agree that we are certainly drilling quite a few barrels of crude within our own shores. However, considering both economic conditions as well as the motivation and intent of large oil companies, I would not have expected gas prices to decrease at any significant rate (we also need to consider that a good amount of the per-gallon price of gas/diesel at the pump is taxes).

            My argument concerns what sacrifices are to be made in the ‘chase’ for lower fuel consumption and higher MPGs. Regardng hybrids, clearly the Pruis cannot tow as much as my Tundra – nor, can any hybrid truck (e.g., Chevy’s Hybrid Silverado). So, towing capability is compromised. Also, with hybrids/electrics, there is the issue of battery life and disposal – a points deduction to the eco-friendliness of those vehicle types.

            Also, foundationally, fuel efficiency / higher MPGs are directly influenced by vehicle weight and aerodynamics. In the effort to reduce weight, less metal may be used, compromising the structural integrity of the vehicle (which is especially concerning for ‘work’ trucks). However, for non-structural elements of a vehicle, I do like the idea of using aluminum, carbon fiber, and fiberglass to reduce weight. Aerodynamic improvements are somewhat limited for pickup trucks, as the basic of the vehicle serves a purpose (i.e. large engine bay, bed, wheel well clearance, cab height, etc.). My Tundra is already 20 feet long. Trying to impart a wedge shape to the front or back of the vehicle would impractically contribute to OAL. So, pickup trucks will, by design, lose points on the aerodynamic scale.

            To your point “We have chronicled in the past on this site how the more you weigh, the worse fuel economy you have. That’s a fact.”, I would advocate less Big Macs and more exercise. 🙂

            As always, I appreciate the civility of your dialogues. Can’t say we find that on other automotive blogs/forums.

            P.S. I have a hankering to break out my VHS copy of the Road Warrior (or even Mad Max Beyond Thunderdome). It presents an interesting, albeit slightly fantastical, theory on what the world might come to if we become almost entirely reliant on one form of energy and do not at least explore alternative energy resources for our everyday needs.

          • BriBri,

            A VHS of Road Warrior! That is pure 80s gold. 🙂

            I agree with most of what you said. It is an interesting debate about structural integrity versus weight savings and the dangers of these ideas. Hmm… where have I heard that before? Oh yeah, right here on this site!

            One thing to keep in mind though, in the mind of the EPA and most truck builders, the true “work” trucks – HD, Diesel 250 or 2500+ models – are exempt from CAFE standards. It really only applies to half-tons and smaller. So… those “work” trucks won’t be affected, HOWEVER, consumers using a half-ton for a big tow job or a true “work” application, there is an argument to be made that it won’t be as durable/strong as it could be.

            The other aspect of the gas/tax debate is the tax breaks given to oil companies in this country. To be blunt, oil company subsides should end if they aren’t helping lower gas prices for the average consumer, period.

            The battery life and disposal issue is definitely a knock on electric cars. I was actually at a Nissan PR event Wednesday where they talked about how they have extended the warranty on the Leaf. Also, interestingly is that the demise of the Chevy Volt is largely false. People are buying these cars, the fire danger was sensationalized by the media and battery issues aren’t deterring buyers.

            Its funny to hear you talk about how a pickup by definition will struggle with fuel economy. That was basically Sweers’ point to me. There really is just so much companies like Toyota can do to improve fuel economy. This is directly reflected in the way the exterior of trucks are starting to mirror everyone (there is only one tailgate design that is aerodynamic). Trucks will eventually only be distinguished by very minor exterior items and more definable interior changes. Thus, everybody is working on improving their interior.

            Thanks for the complement on the civility, the feeling is mutual. Like I have said, I thoroughly enjoy these discussions as long as it doesn’t become a “you’re an idiot, no you’re an idiot” back and forth. 🙂

            I see your raise and I raise you two more. Do you call or raise again?!


          • AHouse says:

            Two words to destroy your more drilling to become more oil dependant…. “More Refineries”! Thank you this is our real issue.

  24. […] This link is to Tundra Headquarters where I found some facts about the Flex Fuel Engines that were interesting. Five Things You May Not Know About Flex-Fuel Engines | Tundra Headquarters Blog […]

  25. […] Tagged: 0 Thread(s) Quoted: 52 Post(s) All you need to know about FFV's in general. Five Things You May Not Know About Flex-Fuel Engines | Tundra Headquarters Blog 12' CM Tundra, SR5, 5.7L, 4×4 14' Tacoma TRD Sport LB 4×4 ColoradoTJ is online […]

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