I'm not an expert in this, but I assume Stihl engineers are. I own
timberland and have a variety of Stihl and Husky power tools, ranging
from the small "home trimmers" to professional brushcutters, chainsaws
and pole pruners.
Stihl states quite clearly in their owner manuals that 89 octane or
above is to be used, at least with all the equipment I have. You can
read the manuals online at http://www.stihlmanuals.w1.com
They state specifically that lower octane ratings may cause higher
temperatures in the engine and increase risk of piston seizures.
Considering that when I do run my equipment, I often run it for five
hours or so, I would rather keep it cooler, so I spend the extra dime a
gallon and get premium for my equipment.
So, run the higher octane fuel (89 or above) if you trust Stihl. If
You are absolutely correct, you should ALWAYS go by the owner's manual -
never what a salesman in the store says. As to what we say online,
newsgroups are an excellent resource for information that you might
otherwise not know, but always start with the owner's manual.
But WHY should you always follow the owner's manual (or at least CLAIM you
followed the manual)?
a) You may void your warranty if you don't follow the instructions and
b) You have an unassailable position when the device - used according to
detailed directions - maims you.
"Dear Augustus Stihl:
I done used your chain saw and put in 89 octane gasoline and the tree I
cut fell on my truck, completing destroying the vehicle. Since I
followed directions and used the proper grade gasoline, I feel your
company owes me a new Ford F-150...."
Echo recommends 89 octane gasoline, so I usually use mid-grade gas when
I mix a can of 2-cycle fuel.
I've found that if I buy a gallon or two of premium in the spring for my
4-cycle small engines (lawnmower and tiller) they start and run much
better for that first startup. (they usually have a little bit of stale
gas in the tank leftover from the previous year.) By the time I use up
that first can of gas, I switch to regular and they run just fine on 87
octane. All grades of gasoline are 10% ethanol here.
I presume your string trimmer is 2 cycle. Gas and
oil are mixed. What do you think adding oil to
gas does to the octane? What do you think a
slight miscalculation in mixing the oil and gas
will do to octane?
You are right to be surprised. It is amazing how
much BS some people spew. "Cleaner, filtered
more, and lower octane gumming" are all nonsense
that an uneducated person would say.
What you need to read is not on the net but in the
manufacturers handbook. Almost all small engines
2cycle or 4 cycle use regular gas. Most
automobiles use regular gas.
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