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reformulated gasoline


Marc P. Cyr

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All depends but six months is a good stretch. I have some go as long as a year. No bets when it comes to two cycle. Gas and oil mix without stabilzer, about 120 days. Nothing scientific, experience.
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Marc, Bob's answer is right on the money on the 2-cycle mixes. At the shop we see a lot of 2-cycle equipment gummed up or with stale gas that has only been in the tank two to three months. As for straight gas, six months seems to be about max before it starts to go stale. When we had the storms back in June we were overrun with generators that had sat since new(some for 2-3 years) without being started on a regular routine. A lot of unhappy people that went without power for up to two weeks and a generator they could not use! Seems like we had somewhere over a hundred in for service at one time.
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Hi, Stihl and many of the other 2 cycle companies say 30 days is the life span of gas in a can. A factor that is not often considered is that gasoline is constantly reformulated for the climate in the area. This is due to emmissions compliance. It is my understanding that in our area of the country there 8 major formulation changes through the year. Gasoline that is blended for July here is modified to not have the volitiles vaporize rapidly when it is stored. If you put it in a snow blower from a can in July it is almost like diesel fuel. Ad this to the fact that the fuel has aged and lost a lot of the volitiles, and the snow blower won't start. Big engines and 4 cycles are more forgiving in this area. Now lets look at gasoline formulated to work at 0 and below in this area. It is formulated to vaporize at low temperatures and if you keep it in a can and it is exposed to Summer temperatures the volitiles are gone and it again behaves about like diesel fuel in small 2 cycles. I believe if you look at the current owners manuals for Briggs and all of the other small engine manufacturers you will see that almost all say no gas over 30 days old and if you have to use alcoholic gas to drain the carb and fuel system as soon as you shut the unit down. Stabilizers work by forming a microscopic coating that stays on top of the fuel in the tank like laying a sheet of Saran wrap on top of the fuel to reduce evaporation. Agitating the fuel defeats the effect of stabilizer. If you have old gas and put stabilizer in it, you still have OLD FUEL with stabilizeer and it may help it from behaving older. It does nothing to make the gas better. What I am relating here is what I have been told in engine service schools. I very well may be wrong on some of this, and if there any chemical engineers or fuel specialists that think I am like a 6 pack without the little plastic thingy that keeps it all together. they may well be right. I would welcome their input. I am singing the song that is basic in most service schools. I do know that 2 cycle snowblowers do not like Summer gas from this area. My 2 cents worth and its free, value accordingly. Al Eden
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Al thanks for stirring the cobwebs in my feeble brain. I should have passed on the info from Sthil as we quote that all the time at the dealership. In real world time you can sometimes get by with three months but may lack some performance.
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Al once again your 2 cents is an excellent value! I work as an Environmental Scientist and deal with air quality issues daily. My understanding is there are numerous custom blends for various regions of the country and time of year. As a rule of thumb 30 days is the limit. Personally, I try to keep as small of quantity on hand as I will use in 2-3 weeks then if I don't use it in the small equipment, I pour it in the truck and buy fresh.
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