Chainsaw Fuels for Long Term Storage, by Tunnel Rabbit

Even if I do not have time to lay out all that I know about long-term storage of various fuels and the various types of engines that might consume that fuel, perhaps I can pass along some helpful information.

As a rule of thumb, I figure I’ll need one gallon of chainsaw gas for every one cord of wood that I cut, and I’ll need half that volume in bar oil. If we can keep a chainsaw running, then that fuel could be of adequate quality to run anything else. Gasoline is much more difficult to store than diesel, and if we can successfully store gas that meets the higher standard needed to run a modern chainsaw, then we can run anything else with that gas. However, we could also go electric and run a diesel generator to charge an electric chainsaw, but I simply do not have the excessive wealth for that option at this time. Another way is to have a large enough PV array to charge an electric chainsaw. If I could, my first choice in an electric saw would be a Makita, yet as it is, my best choice is an old school, slow and heavy 35 year old saw that I believe is a better choice as it can run on lower octane fuel and a variety of 2 cycle engine oils, even 30 weight motor oil in the fuel in a pinch. But then most already have a modern chainsaw, and so do I, so we’ll need fuel for these.

The old, slow, and heavy saws have their virtues. The most noteworthy is that in a long-term collapse scenario, it can run on low octane fuel that might harm a modern saw. Unfortunately, it would be difficult for the average person to locate or repair an old school saw, so they must contend with the fuel requirement of modern lightweight, and high-performance saws. The problem for modern saws is its requirement for high octane gasoline. Without that, the engine can overheat and become damaged. If you run a modern StIhl saw on low octane gas, or even with fresh premium fuel with too much 2 cycle oil in it, the octane rating is too low. When run hard and hot, one might hear pre-detonation (knocking) in the cylinder that can burn a hole in the piston over time, or immediately. These are high-performance machines, akin to a Formula One race car. There is little tolerance to less than ideal fuels and lubricants. My old school saw is more like a tractor in comparison. It is harder to use, but keeps on plowing through wood, decade after decade with whatever I put into it. The brand and model of my old saw is not important, it is the technology that is used in these saws that is important. Currently, I am running 2-year-old untreated (not stabilized) premium non-ethanol fuel it with a 32 to 1 ratio mix of TW3 rated 2 cycle oil that is not recommended for modern chainsaws. This fuel would not work well, and would probably damage a modern saw and certainly degrade it’s performance. Old school saws are much less ‘picky’ in other ways as well. I have gallons of TW3 type 2 cycle oil intended for water-cooled 2 cycle engines that I got for free. It is higher grade lubricant than was available when the old saw was made.

A modern saw should use a 50 to 1, or a 40 to 1 mixture with a synthetic lubricant for best performance and longevity. Stihl requires 50 to 1 and premium fuel. It is also important to use non ethanol premium grade with an octane rating of 91. Because the ethanol is hydrophillic, and water can be absorbed into fuel during storage. Water suspended in the fuel by the ethanol does not mix well with 2 cycle lubricating oils, and damage can be done to the engine. Water can also accumulated in any fuel tank or container. When filling the saw fuel, always leave about an inch of fuel on the bottom of the gas can to avoid putting water that is at the bottom of the fuel into the saw. Any water in the fuel could quickly damage the piston and cylinder wall. Benzine, not the ethanol can do damage by shortening the life span of the diaphragm in chain saw carburetors. Have several replacement complete carburetors. Gasoline from the 1960s and 1970s was closer to pure gasoline. Old school gasoline did not have near the list of additives, such as olifins that gum up works, and other additives. As time progress, more additives were added for various reasons. The diaphragm is the fuel pump for the saw. Using gas that does not harm the diaphragm, or plug up the very fine orifice inside these tiny carburetors improves reliability and performance. Also octane rating becomes lower as the stored fuel degrades in general. Oxygen is the primary enemy of gasoline. If the can breathes, or is permeable to oxygen, as are plastic storage containers, the rate of degradation increases. Swings in temperatures cause not only condensation, but more import, unacceptably high internal pressures that may cause essential light violate gases to escape containment.

Before this short essay becomes lengthy, discussing boring technical stuff, I’ll cut to the chase, and provide a short list of what fuel to store, from the most desirable to the least desirable.

Aviation fuel

Av gas, 100LL (LL = low lead), my top choice.

Very high octane fuel, such as 100ll ‘av gas’, will cause chainsaws with standard compression ratios to run slower, because the octane level, when fresh, is actually too high. The result is a loss in performance. Fortunately, as this same fuel degrades and looses octane over time, the saw will run faster, and at the speed effect on engine performance. MA, (In My Analysis) this is an acceptable trade off, if the goal is fuel intended for long term storage. The lead may provide a slight amount of lubrication to the piston. It’s primary reason for it’s presents is to increase the octane rating and otherwise improve engine reliability. Many who run av gas in snowmobiles find it’s performance to be superior, and even more preferable than racing gas. The reason Av gas stores so well is that there are few additives in it, and therefore it will not degrade like standard gasoline. This is very good property to have if used in aircraft. Gummed-up carburetors could degrade performance and at worst, engine failure. It is a fuel that is designed to store for long periods of time, because lives are a stake. It is closer to what is pure gasoline once was in the early 1960s, and does not ‘gum up’ carburetors. After much investigation, reading reports from pilots discussing this issue, I believe that if av gas is stored in air tight metal gas cans that are designed for the purpose in an environment that is relatively stable in temperature, this fuel can be remain usable for 5 to 10 years. I use old military jerry cans for long term fuel storage. Because of a shortage of funds, I also use plastic cans, but will use this fuel first as it does not preserve the fuel as long as airtight metal containers. Av gas is inherently stable, so that a fuel stabilizer is not necessary.

Av gas price for 100LL in the U.S. are as of June 5, 2021, are approximately $5.00 per gallon in most states, less than one third to one fourth the price of ‘engineered fuels’.

‘Engineered’ Fuels are a distant second choice

The term is ‘engineered fuels’ is used by marketing to describe a niche category of gasoline fuels available at the big box home improvement store to the local chainsaw dealers. IHMO, their proprietary blend begins with the same stock from the refinery as Av gas is made from, and little more is added than a 2 cycle oil, if the product is intended for 2 cycle engines. The lower octane rating of 92-93 is better suited for maximum power output for a chainsaw, however, the high octane rating of Av gas is a significant advantage if the time in storage might be well beyond the suggest use by date of engineered fuel producers. Av gas is also one fourth the price of the least expensive ‘engineered fuel’ that is the Trufuel brand, and one eighth the price of the highest priced offering in this category. This is why it is my top choice. Given the relatively low price, and the much higher octane rating, I will gladly provide the container in which to store it.

There four major brands, Husquvarna, Stihl, VP, and Truefuel. There is no significant difference in terms of performance and shelf life.
Because Trufeul is fraction of the cost of all the others, roughly one third the price, I can ignore all the others. Trufuel claims a 5 year shelf life if the metal container is not opened, and a 2 year shelf life if the container is open and partly used. I would expect at least a 2 year shelf life if stored in the tank and fuel system of a chain saw. I would not expect to see the carburetor gummed up, or the fine passages inside the carburetor to be blocked if any of these, and including Avgas is used. Thus the reliability will be greatly improved, and maintenance costs greatly reduced. The most common cause of chainsaw malfunctions are the result of partially gummed up carburetors, and damage done to the diagram of chainsaw carburetors by the benzine in standard pump gas. Avgas does not contain but a very small amount benzine. I can only surmise that the various proprietary blends of engineered fuels do not as well.

Trufeul 40:1 mixture at HomeDepot, $17.97 per 110oz can when 4 or more are purchased

Trufeul 50:1 mixture at HomeDepot, $17.97 per 110oz can when 4 or more cans are purchased

Premium unleaded non ethanol automotive gasoline, is a very distant third choice.

The price per gallon in my region is currently $4 per gallon. It is a much better choice that the unleaded premium grade. It contains all the additives that degrade a gasoline except ethanol. I cannot recommend it for modern chain saws if this fuel is stored for more than one year if the saw will be run long and hot. Listen for pinging, or pre-detonation. If an unusual sound is heard when the saw is run hot, let it cool off, and then run it for only a shorter duration. Shorter runs will also be easier on the bar and your back as well.

Concluding Remarks

Avgas at my local airfield is about $5 per gallon, and is far superior choice over all other choices, yet is the least accessible. However it is worth the extra effort to obtain it if it is intended as a fuel for long term storage for a chain saw. In any cost benefit analysis, it is by far the best choice.