10 Mogas myths

The GAfuels Blog is written by two private pilots concerned about the future availability of fuels for piston-engine aircraft: Dean Billing, Sisters, Ore., an expert on autogas and ethanol, and Kent Misegades, Cary, N.C., an aerospace engineer, aviation sales rep for U-Fuel, and president of EAA1114.

Evidence of the growing interest in the use of affordable, lead-free, ethanol-free autogas, AKA, “Mogas,” in General Aviation is evidenced by Ben Visser’s recent article on the topic, The fuel of the future: Is it already here? and the results of a survey conducted by AVWeb. Further evidence is the overwhelming interest we’ve experienced to the introduction of the Aviation Fuel Club, the new Sport Fuel program, and thousands of comments on our petition calling on a ban of the blending of ethanol in Premium gasoline. There remains, however, some confusion about the pro and cons of using Mogas, something we hope to dispel below:

Myth #1 – Gasoline used in airplanes is unsafe. Fact – International standard ASTM D4814 is used for both fuel production and engine TC/STC certification. Mogas has been an FAA-approved aviation fuel since the 1980s and has had an excellent safety record.

Myth #2 – Gasoline is unstable. Fact – Modern gasoline remains stable for at least six months. Addition of some fresh fuel “rejuvenates” old Mogas. Adding ethanol to the fuel dramatically reduces its life.

Myth #3 – Gasoline is not as “clean” as 100LL. Fact – This is a problem of the past mostly eliminated through modern filters. Modern RFG (Reformulated Gasoline required in many parts of the US) is the cleanest burning gasoline made.

Myth #4 – Seasonal/regional formulations cause problems. Fact – Provided fuel remains ASTM D4814 compliant, this can be managed.

Myth #5 – Mogas is less “powerful” than 100LL. Fact – 91 octane E0 Mogas has 3%-5% more BTUs/gallon than 100LL. Lead deposits from 100LL can reduce power, though.

Myth #6 – Higher octane is always better. Fact – Only if needed for anti-detonation. Octane does not increase power. Higher octane is always more expensive, though.

Myth #7 – You can’t find ethanol-free Mogas. FactPURE-GAS.org lists more than 2,600 sellers across the country. The Aviation Fuel Club will help you find suppliers who deliver to airports.

Myth #8 – Gasoline producers won’t sell E0. Fact – Perhaps not at retail stations, however many fuel terminals around the country sell ethanol-free fuels to airports, marinas, farms, etc.

Myth #9 – A Mogas pump is too expensive. Fact – The Aviation Fuel Club will help find low-cost options, which might mean a small military surplus fuel trailer. U-Fuel has developed a line of smaller, self-service Sport Fuel stations ideal for GA airports wishing to add mogas.

Myth #10 – Mogas at airports costs too much and takes revenue away from airports. Fact – Mogas is typically $1-$3 cheaper than 100LL and makes its seller a profit. Airports selling mogas recoup revenue lost to self-fuelers, help sport aviation and flight schools grow, and retain the same flowage fees as 100LL sales. They also make real reductions in lead emissions, a serious public relations issue for General Aviation.


  1. Ernani Seddon says

    Ethanol from corn can be subsidized but the new 2 generation alcohol from cellulose will be coming into age and thta will make it cheaper. Dennis is correct the aircraft manufacturer should be facing the fact that the market is in an ever changing process.. My experience with 100% ethanol powered aircraft can be resumed as:
    Ethanol generates more power, but spends more fuel per hour.
    In Brazil is cheaper to run than Avgas, crop dusters claim it saves 25% more money in the end
    The engines last longer and has less problem. 100 hours spark plugs look as if they were brand new
    CHT is lower
    I have seen many people flying with out any corrosion problem.

  2. Phil says

    I’m a newbie to aviation but built a zenith ch 750 and installed a dont 0-200A, what fuel can I get away with burning?

  3. Mark says

    Does anyone remember when the petroleum industry bad mouthed gasohol. They said it would ruin car engines. They of course promoted their own fuel additives which were found to be really toxic. So, ethanol blended gasoline is now widely used in cars, light trucks, small tractors, and gas engines of every size. I hear no horror stories except from a few die-hards that refuse to use anything but premium gasoline even though their owners manuals say that 87-88 octane is just fine. I wonder why ethanol can’t be used in aircraft engines?
    I think in a short time, butanol will be economically produced and available for use in internal combustion engines. It can be transported via the same pipelines and infrastructure as is gasoline. It has nearly the same amount of energy as does gasoline. It will be made from all sorts of cellulose products—trees, grass, paper, etc. Theoretically, it should be very abundant and cheap—theoretically!!! As with ethanol, water is miscible in butanol which is good since it will prevent ice in fuel tanks, fuel lines, etc. I am hoping that these alternative fuels help make flying affordable again. Not many general aviation enthusiasts can afford to pay $6.00/gallon for avgas.

    • Buck says

      Ethanol is a bad additive to gasoline, among other things causing shortened shelf life. Ethanol in gasoline can cause it to go bad in as little as 2 months, 6 months being the norm. Ethanol is caustic on fuel lines o-rings and seals. Ethanol being hydrophylic, causes corrosion and water related issues in gas tanks and fuel lines.
      Ninety percent of small engine failures can be attributed to ethanol in gasoline. Especially engines having carburetors which are prone to jet blockage due to the presence of this additive.

      I think many pilots use leaded gas because it has lead as a lubricant, which lessens wear (friction) on pistons, rings, cylinder walls, intake and exhaust valves. Engines consequently run much cooler.

      No wonder avgas is still around.

      • Ernani Seddon says

        I am from Brazil and I see lots of aircraft flying with 100% sugar cane ethanol. Indeed our local FAA equivalent allows agricultural aircraft to use 100 alcohol.
        I personally know of a case of a rancher that for 23 years he flew his Piper Arrow with alcohol in one tank and 100 octane on the other. He took of with normal aircraft fuel in flight he switched to alcohol and use the mixture control to correct the engine performance and went back to aviation fuel for landing. At his ranch he switched the fuel. He empty the alcohol tank and replace it normal aircraft fuel. Took the alcohol and filled the 100 octane tank. He never had any problem. Any one has any coment on using mogas with alcohol?

  4. Jim Smisek says

    Just came across this by accident and had to chime in. I have been using Mogas in my daily commuter airplanes since the STCs first came out without any noticeable problems other than on a 110 degree day in Texas after heat soaking the from a 2 hour flight. And that was simply a hard start. Yep, Mogas is used daily (300+ hours/year), Yes I commute to work by airplane. Live on an airpark North of Dallas and commute into Dallas by air – daily using Mogas. I can run my engine 2400 hours TBO (twice) plus without valve problems and typically without interim cylinder change (religious oil changes every 35 hours). Mogas has become more difficult to find but it is out there and fortunate for me from at least 3 competitive sources within reasonable driving range. Mogas is GREAT and using it allows me to commute by air cheaper than by car.

    • Ryan says


      It’s good to hear a success story like this! I’ve been contemplating commuting into Dallas. Any additional details would be greatly appreciated (like where mogas is sold in dfw).


      • Mark says

        I would assume Jim, being on an airpark, has access through the airpark. As I don’t buy 100LL outside except when on longer trips returning, he probably doesnt buy fuel in Dallas. The only mogas on an airport close to you is Winnsboro, so you either must have a storage tank, or use red cans. I live in southwest Arkansas, where distributors are plentiful for E0 mogas. I have my own tank next to my own hangar on a private grass strip convenient to my home. When my tank is low, I have 400-500 gallons brought in. Now, at 2.00 per gallon savings, this is very worth while and pays for annuals and land lease. But….the tank idea only works if you fly regularly, or if you share cost with other pilots, as they may do at Jim’s airpark. That being said, my Cherokee 235 runs great and I figure at 125-150 hours a year, I spread considerable savings to be used on other necessary things. By the way, I now have an EAA member who keeps his plane at the strip using out of my tank. If you worry about fuel stability over months having large volume available in a tank, sharing the usage and expense will turn the tank quicker.

  5. Steve McNew says

    Given the rise in interest in LSA flying, and the cost of fuel as a real deterrent, what I believe that GA needs is more mogas – at my airport, some pilots bring it in, in cans, from a dealer some distance away. If sold here, even from a freestanding tank, I can only believe that our airport would be enlivened.

  6. Choller says

    “Myth #5 – Mogas is less “powerful” than 100LL. Fact – 91 octane E0 Mogas has 3%-5% more BTUs/gallon than 100LL. Lead deposits from 100LL can reduce power, though.”

    You are comparing energy content per unit quantity  (BTUs / gallon) to ‘power’ ‘energy per unit time’. The 100LL will produce more power in a given engine as it explodes faster and therefore can spin the engine faster (given that the engine can be cooled and can handle the extra RPM). So myth 5 is not a myth, it is a fact.

    • Brian says

       HIgher octanes will compress further before spontaneous combustion due to heat from high compression-IE why high performance engines require higher octane to prevent detonation; I haven’t seen anything concluding that the ‘flame front’ of the expanding gasses after ignition moves faster in a high octane fuel. Do you have anything to back up the energy per unit time argument?

    • John says

      Uhh, NO. 100LL burns “slower” than 91 MOGAS. Higher Octane retards combustion, not the other way around.

      Notwithstanding, the idea that if it “burns faster” you’d get a faster spin is also nonsensical. This is an equation of power, not speed. The more power, at the right time, will result in more power transferred to the crank and thus the prop, to overcome resistance/drag/friction, etc. More power will make it spin faster.

      But the issue is really usable power. If the combustion happens too fast, the power it creates can be wasted in the cylinder in one of two ways. Most all 4 strokes are timed to begin ignition prior to the piston reaching top dead center (TDC) in the compression stroke. The ignition timing assumes a combution propogation such that the burn will reach the piston at TDC or just beyond. Too much octane and the burn gets there late, too little and it gets there too early, fighting the piston on its up stroke (i.e. pre-ignition/detonation). Another loss of too quickly burning the fuel is that the combustion can burn out before the piston is done with its power stroke.

      The speed of combustion (by octane) is engineered for each engine and its timing. So, your statement that “in a given engine”, is nonsense. Some engines need more octane and some less. A high compression engine is more prone to detonation and typically likes a high octane to prevent pre-ignition/detonation. This is one reason why people that don’t understand how engines work think that high octane means more power. It doesn’t by itself. It only does in an engine designed for that slower burn (slower, not faster).

      Most planes with MOGAS STC’s were originally certified for less octane than 100LL, so they are designed to run with a faster burn that lower octane provides. They are “timed” for it. 100LL in these engines causes them to burn the fuel outside of the timing they were designed for and thus have less power.

  7. Kent Misegades says

    Tim, no one is suggesting that mogas is a solution for those who need 100 octane fuels. But it is a good solution for 70%-80% of all legacy piston aircraft and essentially 100% of all new LSAs. To ignore affordable, lead-free mogas as an important aviation fuel is irresponsible. To deny millions of Americans whose engines in boats, power tools, old cars, airplanes, etc. can not operate with any level of ethanol is also irresponsible.

  8. Keith Ellis says

    We have used Mogas in our certified Diamond DA-20-A1 for years now. The airplane came from the factory approved for Mogas and the Rotax engine runs better on Mogas than 100LL. Use of Mogas allows the use of full synthetic oil, which prolongs engine life. We have never had any issue with the use of Mogas in several hundred hours of flying the Katana. Diamond and Rotax have both approved the use of up to E10 without limitation, although E0 is preferred.

    • Mike Willey says

      One of the main reasons that 100LL is around is the fact that it IS the only solution for high compression aviation engines. However, as Kent said, MOGAS is good for most all of the low compression CONT and LYC engines and of course the new designs like ROTAX 912 series that were designed to run on MOGAS.. So the bottom line is that 70 to 80 percent of the light aircraft flying can use MOGAS

  9. Tom Clark says

    The true solution to this problem is the two companies that are developing a drop in replacement for 100LL, Swift and GAMI. The aviation industry needs to contavt their legislators and ask them to help with the development of these fuels. If we can get to the Moon and build hoover dam with our tax dillars the Feds can help with this!!!!

  10. says

    We have about 750,000 hours on ethanol – paying $1.50 per gallon – produces 20% more power than gas and extends my TBO from 2000 to almost 4000 hours and my Cessnas are already STC approved for ethanol. This is much safer than gas and better for the engine and much much better for the environment. This is also a big selling point to my customers because we are a Green renewable fuel. The Cessnas were just certified in the Domincan Republic to burn Rum – yes rum – at $1 per gallon. The aviation industry is going down the wrong road trying to recreate expensive gas replacement controlled by a few large corporation I can actually produce my own fuel when I want to take that next step.

    • craig p says

      Bruce, you’ve got some wild and crazy comments on burning ethanol…….Ethanol is less BTU’s/unit which directly means less power. That’s the same reason you will always everytime get less mpg in your car from ethanol. Later model vehicles handle the fuel just fine and it’s cheaper per gallon, but you get less mileage (which may even translate to being more expensive per mile). And doubling your TBO by diluting with 10-15% alcohol…definitely no factual basis for that one. Safe to run – probably so. All the other stuff – definitely not. As for being greener, you are burning people and animal feedstock by using ethanol (corn). So, while it is a renewable source, it directly increases virtually all food prices. Mexico had riots over the increases in tortilla prices (corn). Ethanol is heavily subsidized. If it wasn’t, it wouldn’t even exist because it is a money loser without your tax dollars propping it up (buying it down). And would you get me some of that $1.00/gallon rum while you’re down there? thx

      • Keith the Automotive Engineer says

        Craig, Bruce is correct in most of his comments. It is amazing how many people understand about half of the story. Here are the facts. Yes, you definitely get more power burning ethanol. This is one reason Indy cars burn it. BUT, it does have less BTUs per pound. So how can both statements be true? Simple. You burn more of it per hour. You also can increase the compression ratio if you want to since the octane is higher with ethanol. Remember that octane does not give you more power. Compression ratio does. It is just that you will need to use higher octane fuel with a higher compression engine to prevent destructive knocking. Saying ethanol is bad is like saying diesel is bad. It is just a fuel that requires changes to an engine. That’s all. So what is required? Ethanol is hydroscopic. It absorbs water. Water is corrosive, so metallic parts must be protected against corrosion. That means stainless steel fuel lines and anodized aluminum where it comes into contact with ethanol. This was the major change to Rotax engines when they approved them to burn E10.
        The other change needed is with some polymers. Some polymers will be dissolved. Others are weakened. There are lists online that some automotive companies have provided that list what polymers can be used with what percentage of ethanol.

        The bottom line is that ethanol is not a bad fuel. It is just different.

        Now you know the facts.

  11. Dennis Reiley says

    Finally a good article on the advantages of Mogas. But I disagree on the difficulties of an ethanol blend, which is mostly because of the design of aviation engines and aircraft fuel systems. Every gasoline engine manufacturer or rebuilder should be producing those engines to not only operate with Mogas but also with an ethanol blend. Nothing can be done with current engines, but the aviation industry needs to prepare for the future and there are only a few in the aviation industry that are seriously doing so.

    It’s the attitude of “we’ve always done it this way”, yep they have, all aircraft used to be biplanes and the engines were lubricated with Castor oil too. Not many of those flying today though.

    Ethanol production is subsidized, it is done in the hope that eventually a blend of gasoline and ethanol will be cheaper and better. Whether that will transpire is in some doubt. But the aviation industry cannot afford to be caught unprepared and that has already happened with the move to unleaded fuels. The argument that ethanol deteriorates faster is invalid as there are additives and you should do preventative maintenance on all powered machinery after it has been in long term storage before placing it in service. Aircraft are not an exception.

    Every manufacturer of aircraft and aviation engines using gasoline must face the fact that they must lead or their customers and their competitors will eventually demand they get out of the way.

  12. Philippe DUCROCQ says

    Lead additive available at FBO’s to the small minority of high compression engines would avoid grounding excellent planes and considerably diminish lead pollution by aircraft fleet

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