Gasoline Types and Long Term Storage, by Tunnel Rabbit

I started wrenching in 1976, and have several decades of experience in this field.
Diesel is the best fuel for TEOTWAWKI, but I cannot afford to switch, and I do not have diesel chainsaw.  I store aviation gasoline (Avgas) “100LL” for my chainsaws and generators.  This pure form of gasoline does not separate, nor degrade as rapidly as modern gasoline sold are regular gas stations. It is much like gasoline was in the 1960s that contain lead, and has few additives. You can buy it at most airports that cater to general aviation private pilots. If stored in air-tight metal 5 gallons in a temperature-stable environment, it can run an airplane after many years of storage without the use of a fuel stabilizer. Many pilots report the remarkably long storage life of Avgas.  Avgas in it’s various forms have been used in automotive racing, and as fuel stock for different blends of racing fuel. And it is highly regarded by those who have used it in snowmobiles to chainsaws.
Storage Containers and Management
Plastic storage containers are oxygen permeable and oxygen degrades fuels, so these are not ideal for long term storage measured in years.  The good old metal 5 gallon jerry can is ideal. New versions of this container are expensive and can found in stainless steel!  Reduce storage container cost by using less expensive plastic cans for fuels that will be used first and metal cans for feuls that would be used after many years of storage.  For chainsaws, just one gallon of gasoline can cut a cord of softer woods. Therefore, one expensive or high-quality air-tight metal can might be justifiable, if the fuel will be used after several years of storage.
However, a good alternative to this scheme is proprietary custom fuels such as VPN (best), or others such as Trufuel (much more cost-effective).  These are sold in air-tight metal cans eliminating the need for purchasing such for the purpose of long-term storage of fuels. The high cost of these fuel alternatives are justifiable in my book, if it will be used to run chain saws.  I suspect that the reason these proprietary fuels store so long is because they might be using the same fuel stock that is used for Avgas. But, I cannot prove it.  Besides Trufuel, the least expensive of this category, and runs around $20.00/gal, while Avgas, in my area, is less than $5, and the national average was less than $6 per gallon, when I last checked.  I do have one season’s worth of Trufuel in reserve as a contingency to power a chainsaw.
Avgas does not have the same light volatiles of automotive gasoline blends, so starting could be more difficult in cold weather. It is designed to run an airplane a motor at a steady speed of 2,000 to 2,300 rpm.  The lead in this fuel increases the octane rating, cools the valves,  lubricates valve stems, and cylinder walls as it was designed to do given the soft metal used for engine valves prior to 1972.  It would also lubricate 2 cycle motors.  Chainsaws to snowmobiles love it.  When converted to a metric for automotive fuels, it has a 96 octane rating, and contains a modest amount of lead, therefore it should not be used in engines with emission controls and catalytic converters.  Oxygen sensors in the exhaust system, and the catalytic converters would quickly become damaged.  The vehicle would continue to run, but without the benefit of good functioning oxygen sensors, the motor will run rich and fuel economy would suffer.  Repairing the vehicle, should it need to pass an emissions test in the future, could be expensive. 100LL avgas can be purchased at my local private airport for only $4.99/gal, only 50 cents more per gallon than non-ethanol premium gasoline that is often considered the best gasoline for long-term storage.
Avgas, Mogas, and Chainsaws
I would use not use ethanol fuel for chainsaws for a variety of reasons, unless there was nothing else. And it would be the least desirable and poor choice for long-term storage as ethanol is hydrophilic and degrades the additives in fuel. ‘Hydrophilic’ means water can be absorbed into the fuel and burned. This both good and bad.  Good if it will be run through a 4 cycle motor, such as are vehicle motors, but bad if it will be run through a 2 cycle motor that are used on chainsaws. 2 cycle motors require a specialized oil to be mixed into the fuel. This oil-fuel mixture is used to lubricated the motor and to run the motor.  If there is water mixed in with the fuel, the operator would not know this as ethanol absorbs it, and it is carried in the fuel. The water in this fuel is not a good lubricant, as it does not mix as well with the oil that is added and intended for purpose of lubrication.  A water-soluble fuel does not carry lubricants as well, as a pure petroleum-based fuel does.

Avoid Ethanol Blends
Ethanol will also quickly damage the chainsaw’s flexible diaphragm in the carburetor that acts as fuel pump. The most common cause of small engine failure is ethanol gasoline that have been allowed to remain in a fuel system for an extended period of time.  Non-ethanol fuels are more stable, yet these too will leave a gummy residue that easily plugs up the tiny orifices inside a chainsaw’s carburetor. Avgas does not leave a gummy residue and therefore, chainsaw carburetors will not become plugged up, and will perform as designed over a much long period time, even when stored without emptying the fuel. A chainsaw using this fuel will be more reliable and run better.  My 35 year old Husky loves it, and so do my modern Stihls.
High Performance Motors Require High Octane Levels
Modern Stihl chainsaws are high-performance machines that require a high octane fuel of no less than 91, as per the manufacturer. Otherwise, I believe piston damage could occur. If the fuel is old, the octane rating is lower than when it was fresh. Although Stihl recommends 91 octane, the saw can usually avoid becoming damaged  ‘IF’ it is not run so long as to become very hot, and is not run with a wide-open throttle. Because Avgas is rated at 96 octane, it can age long and retain a higher octane rating after several years of storage.  Lead as a primary ingredient used to increase the octane, does not degrade as other chemicals used to increase an octane rating, therefore, IHMO, Avgas will retain a high octane level for many years.  Whereas unleaded fuels do not have this key advantage. This, in great part, explains why private pilots have reported good performance using Avgas that is well beyond the expiration date for commercial aircraft, and could be considered dangerously past it’s prime for use in any aircraft.
Even if we are using old Avgas, I would not let the saw get too hot.  If I hear pinging, shut it down and let it cool off.  My old Husky saw is not a high-performance machine, and runs slower, and uses a 32:1 fuel to oil mixture.  The greater the concentration of oil in the fuel, the lower the octane rating becomes. If modern synthetic 2-cycle oil is used at a 40:1 ratio, the octane rating would be higher, the saw will be adequately lubricated by the oil, and the lead in the Avgas.  Generally, the old saws can tolerate lower octane fuels much better than modern saws. I suspect the last saws to quit running once the fuel stocks become degraded, will be these old saws.
Mogas (automotive gasoline), when it evaporates will leave a very gummy residue that can prevent the fuel system from operating correctly.  When Avgas evaporates there is no gummy residue, but a tiny amount of dry white powder is left behind. This is the lead. Avgas weighs about one pound less per gallon than automotive gasoline. It is a highly refined fuel, closer to naptha, that is white gas, a pure or highly refined gasoline. White gas used in the familiar Coleman lantern is naptha. It is well known that it can stay good for over a decade in a metal can. Unfortunately, this fuel only has an octane rating of 55, way too low for most motors. However, a small amount might be mixed with Avgas as it has an octane rating of 96, might extend a precious and dwindling fuel supply.
Stabilized non-ethanol premium fuel will reliably start and run a naturally aspirated low compression motor after 3 years of storage.  Avgas, stored in airplanes for as long as 10 years, have been reported by many pilots to start and run small aircraft well.  Pilots are naturally concerned with the quality of the fuel, and reliability in general.  While researching this topic, years ago, I determined their reports to be useful. Either It Starts, or it does not.
Experiments in Reviving Degraded Gasoline
I’ve run 4- to 5-year-old gasoline as part of a blend.  If I only had 4- to 5-year-old fuel, I suspect that the motor would not start. As we should for any gasoline we might choose for long-term storage, a case of ether(quick start) to help start engines on aged stored fuels is would be a wise move. Fuels older than 2-4 years old could need help starting the vehicle or saw, in very cold weather. And gasoline older than that would likely not start the motor, but would in my estimation run.  Regardless, it is better to have it and not need it, than to need it, and not have it. And, with good fortune, we might be able to source a fresher store of gas to make a blend.  Yes, it is true, the solution is dilution, and perhaps a shot of ether.
From my experimentation, 20 percent by volume, or more, of very old fuel, can be added to fresh fuel with only a slight decrease in performance in a low compression carburetor motor.  I’ve even run 20 percent kerosene and diesel in the same gasoline motor. As another future experiment, I might attempt to revitalized old fuel, by replacing the light volatiles by bubbling propane that will go into solution.  This will replaced the lost light volatiles, such as benzine, and help the fuel start motors and improve throttle response.  Because Avgas stores well and has a high octane rating of 96, it can be added to a quantity of old low octane fuel to help revitalize, and use it in a blend.  Running low octane fuel in low compression motors with a compression ratio as low as 7.5:1 is not as problematic as running old fuel in motors with higher compression ratios.  Motors designed for the Third World were designed to be low octane for that reason.  If a standard compression modern motor is used, retarding the timing might be necessary, yet not possible on some modern motors, and performance suffers as well.
Adding alcohol will increase the octane level of degraded gasoline. This was a practice used in early model vehicles to get them to comply with an emissions requirement. The alcohol will also remove water from a fuel tank and suspend it in the fuel and be burned.  The resultant higher octane levels with alcohol, added, are more resistant to detonation, and the vehicle could be drivable without excessive pinging and knocking. We might also experiment with toluene. In a similar way. However, this method might be cost-effective for small motors only.
As a thought experiment, bubbling propane, and adding 90 percent denatured alcohol at a rate of 1 part to 4 parts gasoline at a maximum.  This can be found in a hardware store or in your medicine cabinet.  Combine the alcohol and bubble propane to the old fuel. If the fuel is very old, or not enough alcohol or propane can be used, starting a low compression 4 cycle motor with ether, might work. as a substitute for propane. If not, add a small amount of fresher fuel, or Avgas.  Although mildly dangerous, we might use propane gas to start these and other motors, if ether is not available.  Simply place the un-lit torch end at the opening of the air intake of a EFI motor, or at the entrance of a carburetor, and start the motor.
A Pump for Fuel Transfers
One of the handiest ways to manage stored fuel is an electric fuel pump.  For less than $100 or so, an electric fuel pump will make transferring fuels a breeze, and can pump fuel from an in-ground plastic drum…  Ask your local parts store for a high volume unit designed for a carburated vehicle.  These will be low pressure pumps.  Add an in-line filter,  10 amp fuse, battery clamps, a 25 foot paired 12 gauge wire, and buy good quality fuel hose designed to handle ethanol fuels.  This fuel line is now expensive, but worth it.  A versatile length of hose would be 25 feet. The intake line could be 15 feet in length, allowing plenty of excess line to be fed into the tank of any vehicle. The remaining length of hose can be shorter and adequately long enough to be inserted into the tank of another vehicle. The inline filter should be installed on the output side of the pump as pumps in general do not pickup fuel on the suction side well, and any resistance on that side of the pump might degrade  their performance.
If All Else Fails
I have plans to made a wood gasifier.  FEMA still provides plans for simple version to be used to run a tractor.  As an example of just how easy it could be,  their plan uses 1940s technology, iron pipe, and fittings, and a trash can.  There are many videos of these that were built in back yards. These were used all over Europe during WW2, from tractors to tanks.  A crude version could run a generator.