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Welcome to the STIHL USA Blog

Thursday, March 15, 2012

Gasoline Guidelines for STIHL Outdoor Power Equipment

by Randy Scully, National Service Manager for STIHL Inc.

Gasoline plays an important role in everyday life, powering everything from your automobile to your outdoor power equipment. However, all gasoline is not the same. Knowing a few facts about your fuel can keep the engines in your STIHL equipment running strong. 

What’s the difference between my car’s engine and engines used in small power equipment?

Automobiles have comprehensive fuel and engine management systems controlled by electronics and numerous sensors. You may not feel or hear anything going on when your car is running, but there are many measurements and automatic adjustments being made to account for things like humidity, altitude, temperature and the quality of the gasoline being used.

On the other hand, yard and garden power equipment like your STIHL tools are designed to be compact and lightweight. These tools don’t have the space available for the equipment found in automobiles and so are much more sensitive to issues like fuel quality.
Varnish in Carburetor

Gasoline storage life:
You may not realize it, but gasoline begins to decompose and break down into other compounds in as little as one month when stored. This is not normally an issue for cars since people drive their cars and refill their tanks on a regular basis.

Outdoor power equipment is often used far less frequently, sometimes
as little as a few times in a year, and then can be stored away for weeks, months or years until it is needed again. Additional fuel is normally stored in containers that may only be refilled once or twice a year. This means there is a greater chance of the fuel breaking down and forming gum and varnish-like compounds that can easily restrict or block the tiny fuel passageways used in small engines. 
Carburetor damage from stale fuel

Any gasoline remaining in your storage can or left in your power equipment for more than two-three months can lead to expensive damage to your equipment’s fuel system and engine. This is why STIHL recommends always using fresh fuel or specially formulated fuel mixes like STIHL MotoMix® in your equipment. STIHL MotoMix® is a high-grade, high-octane, ethanol-free
premixed fuel containing STIHL HP Ultra synthetic oil. It is a pure and stable fuel mixture that can be stored for up to two years in the original container and is ideal for machines that are used infrequently. 

What you need to know about Ethanol:
Ethanol gasoline blends have different characteristics that need
to be considered when fueling your STIHL power equipment.      
Damage to carburetor diaphragm

• Much of the gasoline sold throughout the United States contains ethanol. The maximum ethanol content allowed by law for use in outdoor power equipment is limited to 10% (E10). Most small power equipment engines are designed to use no more than a 10% ethanol gasoline blend.

If you are not sure of the ethanol content in the gasoline you are
purchasing, ask the station attendant. If they are unsure, purchase
your fuel from another station that offers gasoline with no more
than 10% ethanol.

 • Ethanol is a stronger solvent than gasoline and can soften, swell and damage some rubber and plastic components that gasoline alone would  not harm.        

Left: Plugged fuel filter screen
Right: Clean fuel filter screen
The solvent properties of ethanol can also dissolve varnish and gum deposits that have previously formed  inside fuel storage cans, fuel tanks or the equipment’s fuel system. When these deposits become dislodged, they can mix with the fuel and plug small openings and filters within the fuel system and cause costly damage to your equipment.

Corrosion inside carburetor
• Ethanol easily attracts and mixes with water, so any moisture in the air can be absorbed by the ethanol gasoline blend. This moisture can corrode metal components in the fuel system leading to expensive repairs. If enough water is absorbed, the ethanol and water will settle out of the gasoline blend. The resulting ethanol and water mixture is heavier than the gasoline and settles to the bottom of the equipment’s tank or your storage can, leaving a layer of gasoline floating on top.

If enough water is absorbed, the ethanol and water will settle out of the gasoline blend. The resulting ethanol and water mixture is heavier than the gasoline and settles to the bottom of the equipment’s tank or your storage can, leaving a layer of gasoline floating on top.

With the ethanol separated from the gasoline, the layer of gasoline now as a lower octane level than the original ethanol gasoline blend. If you originally bought 87 or 89 octane fuel, 
Water and ethanol (bottom)
separated from gasoline (top)
the gasoline layer in your storage container now has a lower octane than what the engine manufacturer intended to be used, resulting in unstable engine operation, power loss and major engine failures.

This separation of ethanol and gasoline can also occur inside the fuel tank of your equipment. Since the fuel is often drawn from the bottom of the fuel tank, the engine is drawing in a mixture of ethanol and water with no gasoline and, in the case of 2-cycle engines, also has no lubricating oil. This ethanol/water mix is thicker than gasoline and cannot easily pass through the fuel system. This can result in hard starting, unsafe high idle
speeds, stalling and can ultimately lead to engine damage or fuel system failure, resulting in costly repairs. 

Guidelines for using E10 gasoline in STIHL power equipment:
U.S. EPA regulations make it illegal to use gasoline containing higher than
10% ethanol content in outdoor power equipment like your STIHL power   
Corrosion from water inside carburetor
equipment and doing so can void your STIHL Limited Warranty.

If the proper precautions are taken, however, gasoline containing a
10% quantity of ethanol can safely be used in your STIHL products.      

•Use a minimum of 89 octane gasoline and always use fresh fuel.
Only buy enough gasoline that you can easily use up within a two month period.

• For air-cooled, two-cycle engines, use a quality mix oil that meets the engine manufacturer’s recommendations. All STIHL oils are designed to
readily mix with gasoline containing 10% ethanol. STIHL HP Ultra Oil is     
especially suited for use with E10 gasoline.                                                    

Seized Piston
 • Shake your gas can well when first mixing the oil to thoroughly disperse the oil in the fuel mixture.

• Gasoline containing ethanol has a tendency to “lean out” the
carburetor mixture when compared to gasoline without ethanol.
Make sure your dealer is aware that you are using gasoline with
ethanol in it so that he can ensure the carburetor is adjusted properly
for the fuel that is being used

• Properly store your equipment. If your equipment is not going to be used for a couple of months, the remaining gasoline in the machine should be drained from the tank and disposed of properly. 

Use STIHL MotoMix®
 To ensure that any remaining ethanol is removed from your equipment, STIHL recommends adding a small amount of STIHL MotoMix® premixed fuel to the tank and running the engine for a few minutes to circulate the fuel through the carburetor. This will flush any of the original gasoline out of the system and protect the fuel system components from water absorption and fuel decomposition. If the machine is going to be stored for several months, it is good practice to empty the STIHL MotoMix® from the machine’s tank, then start the engine and run at idle (do not rev up the engine) until the machine runs out of fuel.

• Equipment should be serviced regularly by your STIHL Dealer. Items such as fuel filters, fuel lines, carburetor diaphragms and spark plugs should be checked and replaced if necessary, as part of a normal engine tune-up.               

By following these guidelines and suggestions, your STIHL equipment               
should perform the way it was designed and help you get the job done. For
more information and tips to help you get the most out of your STIHL, visit


  1. Too expensive at current prices!

  2. I use 100% 89 octane gas w/the Stihl HP oil. Can I leave that in my equipment longer than using gas with ethanol and store in my can longer than the 3 months you recommend? It is getting harder to find 89 octane 100% gas but easy to find 93 octane.Can the ethanol free 93 octane be used in Stihl products?

  3. I just had to have Stihl dealer clean carb on my HT-100 from being stored all winter with (then-fresh) 92-octane Sunoco + Ethanol treatment * Sta-bil in full tank. Dealer charged me $42.00 (including tax, but not including my 16-mile round trip and time spent). Hence, I disagree with first posting's, "Too expensive" -- while at shop I bought five cans of MotoMix. Seems a win-win to have this product which will always keep my saws happy and running well! Yes -- present "gas" is BAD -- but, if the MotoMix addresses and eliminates problems? Hey -- it's all I'm going to be using in my 11 Stihl saws!

  4. 100LL Aviation fuel + Stihl High Performance oil has kept all of my Stihl equipment in perfect shape for the past 15 years. No issues with storage, corrosion, or fuel decomposition. Plastics and diaphrams are not attacked and the engines start instantly. It does not matter if it is hot or cold, or if they have been setting for months.

    1. I have also been using 100LL in all my 2 and 4 cycle equipment from the beginning. Average age of equipment is 15 years and they all virtually start on pull 1. I put fuel shutoff valves on all equipment and when finished with the job just turn the valve to off and let the engine run till it has cleaned out the carb and stops. Have not had to replace any fuel system components.

  5. Thank you for posting this - very helpful.

  6. It is crazy how much even 10% of ethanol can effect old 2 stroke motors. We have had an old 82' Merc. 200hp outboard engine for our boat and because of the increase of ethanol the engine has been running so crappy to the point where it needed a major tune up, and have to use additives to help compensate. I will take this into consideration with my STIHL string trimmer this year. THANKS.

  7. Adding anything to gasoline that impairs milage is a federal crime, illegal, so how come they get away with it. Ethanol does nothing for the envirment, has distroyed billions of dollars in cars, trucks and equipment, and in a depresed economy is forcing americans to use a inferior fuel with very poor gas milage at over $4.00 a gallon.I will never buy anything made with corn ever again.

  8. Ethanol is not a new or bad thing. Its used mainly as an octane booster in fuel because its less hazardous than other chemicals they've used in the past to raise octane levels. The problem with Ethanol is that its such a good solvent, it cleans all the deposits left by gasoline alone. And its hygroscopic, meaning storage of fuel and keeping it air tight is more important now. But think about this, the first vehicles Henry Ford produced, ran on pure ethanol fuel. Alot of race cars run on ethanol due to its high octane level. Ethanol is not a perfect solution to gasoline but its one of the better ones available now. As for mileage, 10 percent ethanol fuel you shouldnt really see any difference (unless you're buying cheap, nearly stale discount retailer fuel). Ethanol has a lower BTU rating than gasoline alone, so you will indeed use more ethanol than gasoline to achieve the same amount of power, which will add up to a little less MPG. Yes, ethanol will dry out non compliant fuel components in fuel systems after some time. But there are plenty of additives on the market that will reduce this problem alot (Ethanol Shield, Mile-Hi, StarTron, Sta-Bil, etc...) But it cant be all bad, I ran both my Snapper mower with a Briggs Intek engine, and my Shindaiwa M-230 trimmer, for about 8 years before needing to do anything to my carburetors. Its mostly all about the quality of the fuel you buy, how well you store it, and that you made sure to put your stabilizer in the fuel while you were pumping it into your gas container.

    1. why use food to make fuel? makes no sense to me. Costs more to produce, lower energy yield, has to be subsidized, and ruins everything. Oh yeah and people starve.

  9. This is a very informative blog about engines, gas and tanks. If you need any oil tank removal Long Island company, I know one that could greatly help.

  10. If your applied in auto financing then this is a great help. We should be well informed on what may destroy our precious cars. Ethanol is not a bad thing, but it can destroy our engine if not properly handled.

  11. Gas production companies with pilot ignition system should read this out to gain some ideas and concept for the future of the oil industry not only in our country but to the overall industry of gas in the world.

  12. I learned that lesson the hard way. To be precise, I lost a lawn mower and a weed whacker I got from an online tool shop because I forgot to drain and clean out the gas tank.

  13. Damian, unfortunately when it comes to fuel these days, it's an ounce of prevention or a whole lot of cure.

  14. One way of maintaining any indoor or outdoor equipment is by putting industrial grease to them to avoid it from rusting cause sometimes when you find it hard to turn this will start up the ruining of the said equipment. It's always better to take precautionary measure before waiting for it to be broken.

  15. It is very important to know and fully understand guidelines such as this one. This is to prevent any damage or loss of equipment. Somehow, the guidelines stated here seems to be like what we are doing as part of taking care at our mazak live tools only the exception of it is not powered by gasoline.

  16. This would prolong the engine of my used Hyundai sonata. I am a self confessed newbie to the automotive industry and posts like this helps me significantly.

  17. I should probably show this blog to my brother before he goes to a car tool store again. That way, he can better take care of the family car and not need to constantly go to a tool shop to fix it.

  18. To maintain the functionality of any equipment especially if it is being used regularly, it should be always checked by experts. This way, you are making sure that your equipment is still at its top condition.

  19. I admit, I didn't know much about car engines until I read this blog. I researched every term and studied it carefully. Now I can keep up with the conversations when my dad talks to his car dealer friends. Thanks for posting this!

  20. Thank you so much for providing this kind of information. This will be very helpful to me since I am planning to apply for a car loan.

  21. Hopefully one does not need to be precise when creating your mixture of gasoline and ethanol. It's too bad if one would void one's warranty due to a mistake.

  22. Thank you for this! I believe it's important for everyone to have a basic knowledge on these stuff. I need it, now that I'm planning to buy a used car. I just think it would help if I know the parts that I need to check before going on with the transaction. Thanks again!

  23. Jacob, glad you found the information helpful. Let us know if there are other topics you would like to see covered.

  24. The clarity in your post is simply excellent and I could assume you’re an expert on this subject.

    Used engines

  25. Thanks a lot for sharing this great information. Everyone should keep these guidelines in their mind to save fuel, money and their lives. People should also learn some car repair tips, so that they can fix their car in emergency situations. Just look onto online car maintenance tips here are some tips and guidelines you should learn!

  26. Your post was good and the information that you giving your post that was really cool. I like it very much. Thanks for posting this. Please share more information and I will bookmark to my blog http://www.plandor45.com/

  27. Glad you found the content helpful. Let us know if there are other topics you want us to cover.

  28. Wonderful, what a blog it is! This webpage provides useful data to us, keep it up.
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  29. I some what knew this but good to read the facts

  30. Use a minimum of 89 octane gasoline and always use fresh fuel only buy enough gasoline that you can easily use up within a two month period. James Karim

  31. Having the appropriate safety gear on hand in the woodshop will make for a safer work environment. Here are a few safety items to consider keeping on hand:This blog

  32. I really congratulate the writer for creating such an impressive blog. Thank you for your valuable discussion on this great topic.

  33. Without this type of guideline we cannot successful. I have read you instructions clearly and should be follow them

  34. I read the article, It is very excellent and helpful. It is lucky to land this website! :)
    Using the right type of fuel is very important.
    1. Read manual (important)
    2. Choose right container
    3. Go premium (do not use the cheap stuff)
    4. Use a 50:1 gas and oil mixture
    5. Shake things up
    6. Storing the mixtures of gas and oil
    chicago blog.

  35. I really congratulate the writer for creating such an impressive blog. Thank you for your valuable discussion on this great topic.

  36. I agree with one of the comments here to put a bit of grease to the machine parts to avoid rusting. That's what I have been doing for a long time and helps a lot to keep my tools rust-free!

  37. Good information,I am avid of any information related to power tool

  38. Great that you are telling the world that gasoline can and will go bad! I had to learn this the hard way. I had gotten this odd felling gig and had not used my stihl in over a year. You should have seen my eyes as i tried and tried to get my saw going! Fortunatly i could run to a pump and get some fresh gas :)