small engine: use "premium" gas?

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I just bought a Stihl string trimmer, at a dealer. I'd read on the net that Stihl engines require at least 89-octane, but hadn't seen anything about that in the literature. So, I asked.
The sales guy said that they didn't _need_ high octane, but you should _use_ "premium" gas ("93"), because it's "cleaner", that it's filtered more, and that "cheaper" gas would gum up the carb.
I was a little surprised at this, but there's a lot I don't know. I don't see where he had any reason to lie - I was already buying the thing.
Does anyone know whether there's any truth to this?
Thanks, George
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You dont need the expensive stuff, read the manual.
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i would err on the premium side, and pay the extra $0.28
that's what i put in my lawnmower, whether it needs it or not -- and i've got the fastest mower on the block
waterboy
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FWIW - My Husky chain saw manual specifically states not to use premium as it tends to make the engine run hotter....
your mileage may vary.
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I think it is BS. Cleaner?
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It is BS. Premium gas is regular gas with Octane added. Nothing is removed. Gas is as clean as the tank and pump filters at the station you bought it.
There is no high compression in a 2 stroke engine that causes engine knocking (pre ignition) that you would need higher octane to prevent.
If you wanted a gas with a detergent in it, go to the parts store and buy a bottle of additive and add a tablespoon or so to your gascan
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Is the motor a 4 cycle or 2 cycle????
Thinking about it, I would just use the 87 stuff and be happy with it. Normally a higher octain fuel is used in higher compression motors. The little engines are normally for from that.
Tom
George wrote:

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The only difference between high and low test fuel is the octane rating. I'd be surprised if the trimmer needs more than 87 octane.
I doubt the sales person was trying to mislead you, but sales people are notoriously ignorant.
-rev
George wrote:

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You can actualy have problems with high octane and vapor lock, many small motor manuals state do not use high octane. The sales guys an idiot.
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Why must you be so redundant? ;-)
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George wrote:

Go by what the manual says or buy the cheapest stuff you can find. You only need to use higher octane fuel if you are trying to shave off a tenth in the 1/4 (with corresponding timing adjustments) or have a radial engine. If you are driving a car so expensive that it needs 93 you have the money to hire someone to cut your grass. High Octane = BS
http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm
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George wrote:

sales guy has no clue. high octane is only needed for high compression and advanced timing, something no trimmer has. Also, my experience with sports cars that I put away in the winter is that high test evaporates more quickly, so I always put a half tank of regular in in the fall, and they fire right up in the spring. WOuld seem a nuisance to do such in a lawn implement
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Directly from the horse's mouth:
See item 13, in particular: http://www.chevron.com/products/prodserv/fuels/bulletin/motorgas/8_q-a/#22
Only very high performance cars benefit from "premium", otherwise it is a waste of money. Certainly a waste of money for anything that uses gasoline around the house.
You may also find the item of interest that refers to how long you can keep gasoline.
--
Walter
www.rationality.net
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Here is the definitions of Octane rating
The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.
Premium gas has small amounts of ethanol to help clean deposits as well a absorb water in the tank. It isn't CLEANER gas by no stretch of the imagination - it's all clean. It might burn cleaner, but this isn't a car, its a trimmer that doesn't have a catalytic converter nor a complicated exhaust system.

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And probably dumping partially burned 2-stroke engine oil out the muffler.
Ordinary ethanol blend fuels have the same octane ratings as regular, and usually cost about the same. The ethanol they have is a lot more than "a small amount" (I think they can be up to 15%).
--
Chris Lewis, Una confibula non set est
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Chris Lewis wrote:

There was a time when "premium" gas had a different detergent package than "regular" or "economy". That may still be the case, but with electronic fuel injection the norm these days it all has enough to keep the injectors clean, which is more than any carbureted engine is going to need.
--
--John
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Let me expand on that just a bit. Higher octane gas is harder to ignite. Like he said above. That also means that a gas engine running higher octane is harder to start. I picked up this slant on it reading a Ford Service Manual. "If the customer complains of hard starting, be sure that they are running 87 octane as specified and not premium."
Charlie
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George wrote:

Many Stihl chain saws require premium gas for the higher compression to get the needed power. Sounds like the salesman was applying this to all Stihl products, which isn't true.
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George wrote:

The sales guy was trying to do you a favor, but he has bought the advertising from the oil companies. Regular is just as clean as premium. Filtering will do absolutely nothing to prevent gumming up a carburetor.
--
Joseph Meehan

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On Fri, 16 Jun 2006 12:15:44 GMT, George

On a well-tuned small engine regular gasoline works fine. I buy the premium blends for all my lawn equipment, not because this was recommended, but I have noticed a difference in the sound and usage of gasoline. I can mow my entire lawn (half an acre) on one tank of premium gasoline, but on lower octane blends I usually have to fill up the tank again. I'm convinced the higher octane is better. You may want to experiment a little bit.
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