2 Stroke Oil Mix - Did I or Didn't I Mix

[Ashful]

Good info. I bought my Husqvarna 359 second hand so I never read a manual. I will start running the higher octane. I would assume it will give the saw a little extra grunt.


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I think it's more about increasing the ignition temperature to prevent pre-detonation (i.e. pinging) due to high compression, which can cause damage to the saw. I don't know that there's any relation between octane rating and horsepower.

 

[jatoxico]

I think it's more about increasing the ignition temperature to prevent pre-detonation

My understanding as well, though I don't count myself as an expert.

 

[saewoody]

I would imagine that if it is running more efficiently because it is not pinging that would result in more power output. I'm not expecting miracles in terms of power, just that the saw will hopefully run a little stronger than it already does.


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[WoodyIsGoody]

This. I never go to the gas station to fill my 2-stroke cans unless I have the 2-stroke oil with me, and add it at time of filling. It's just too easy to forget, otherwise... as you have just found out!

I dump questionable gas into my mower, not my car. I love my car too much.

Running 25:1 will increase plug fouling and carbon build-up. It won't kill your saw, but why not just burn it in the mower or tractor, instead? It is mowing season, now.

Yes. Most use 93 in their saws. Most manuals (eg. Stihl) call out 91 minimum, and they burn so little, why not follow it?

Stihl calls for "mid-grade unleaded gasoline with a minimum octane of 89 (R+M/2) and no more than 10% ethanol content." This has been true for decades and is still true on the new Mtronics.

I've run 89 on my 026 for the last 20 years and am really pleased with it's power under extended load at full throttle. It's a real screamer. Higher octane won't give you more power, it will reduce power ever so slightly. More power can be had by running alcohol free gasoline.

 

[WoodyIsGoody]

I think it's more about increasing the ignition temperature to prevent pre-detonation (i.e. pinging) due to high compression, which can cause damage to the saw. I don't know that there's any relation between octane rating and horsepower.

Actually, higher octane fuels burn with a slower and cooler flame front and this slower/cooler flame reduces peak cylinder temperatures which does help reduce pre-ignition but higher octane fuel naturally needs a higher pressure/temperature to ignite so this is the primary reason why you should not run a lower octane than recommended by the manufacturer.

 

[jatoxico]

Keeping in mind that most ICE's specify a minimum octane, more octane above the recommendation isn't of any particular help in power but anything below can hurt or even damage.

Since stored gas can (reportedly) lose a few points I usually buy premium if the gas isn't going to used right away.

 

[Ashful]

Stihl calls for "mid-grade unleaded gasoline with a minimum octane of 89 (R+M/2) and no more than 10% ethanol content." This has been true for decades and is still true on the new Mtronics.

I just went and personally checked my original 064 manual. It calls out 90 minimum, in clear black and white letters. Around here, our pumps are 87, 89, and 93, so I always buy 93.

Edit: I just checked the online (newer revision) manual, and it also says 90 minimum, but then they added a note in parenthesis saying "(USA/Canada 89 minimum)".

I suppose I could pump 89 octane, and then worry how much it drops during the weeks it can sit in the can before I use it, or I can pony up an extra dollar per year for 93, and know it will likely remain above 90 at the time I actually use it.

 

[WoodyIsGoody]

I just went and personally checked my original 064 manual. It calls out 90 minimum, in clear black and white letters. Around here, our pumps are 87, 89, and 93, so I always buy 93.

Edit: I just checked the online (newer revision) manual, and it also says 90 minimum, but then they added a note in parenthesis saying "(USA/Canada 89 minimum)".

I suppose I could pump 89 octane, and then worry how much it drops during the weeks it can sit in the can before I use it, or I can pony up an extra dollar per year for 93, and know it will likely remain above 90 at the time I actually use it.

1) I have no qualms running higher octane than required.
2) The discussion was about the manufacturer's minimum octane requirements for a Stihl MS 261 which the owners manual says "mid-grade unleaded" w/ min. octane of 89 (R+M/2). That is true for Mtronic or pre-Mtronic. The discussion was not about whether one should run higher than the manufacturers stated minimum. There could be valid reasons for doing so and fuel does slowly lose octane sitting on a shelf.
3) I've been buying Stihl products for over 20 years and every owners manual has been consistent on this 89 (R+M/2) minimum. I still have and use all of the Stihl tools I've purchased. They all start and run great on 89 and run (seemingly) forever.

So, I'm not sure where the 91 minimum octane figure came from. Octane ratings in other regions are typically on a different scale than U.S. pump octane rating of (R+M/2) so that could explain part of it. Now I'm curious, the 064 manual that call for 90 (but 89 in U.S), does it specify the octane measuring system? Every owners manual I've ever seen does specify that.

Much more beneficial than moving up the octane scale above the manufacturers minimum octane would be to insure the fuel you're getting is actually the octane you think it is. Like others here, I always put the first couple gallons in my car to clear the pump of the standard grade fuel before I fill my puny little 1 gallon gas can for my saw and yard tools with 89. I see nothing wrong with using 91 or 93 octane but, if you don't clear the line first, you might actually be filing your 1 gallon can with 87 octane! Stihls own pre-mix gasoline is 93 octane and I'm sure one reason for that is because they know it might sit on the dealers shelf for a long time (at $30/gallon, wouldn't be surprising).

 

[jatoxico]

but higher octane fuel naturally needs a higher pressure/temperature to ignite

Not to get nit-picky but I'm not sure this is exactly right. I understood that higher octane fuels don't need high pressure (compression) to ignite but they won't ignite under high compression like a low octane fuel would. Its the higher compression that makes the power not the gas per se.

If high octane fuels needed high compression then cars only requiring 86 would not run on 93 which is not true, its just a waste to run the 93 in a Corolla.

 

[WoodyIsGoody]

Not to get nit-picky but I'm not sure this is exactly right. I understood that higher octane fuels don't need high pressure (compression) to ignite but they won't ignite under high compression like a low octane fuel would. Its the higher compression that makes the power not the gas per say.

If high octane fuels needed high compression then cars only requiring 86 would not run on 93 which is not true, its just a waste to run the 93 in a Corolla.

I should say higher octane fuels need a higher pressure/temperature curve to SELF-ignite. Once you give it a spark it typically has all the temperature it needs to begin combustion. Because sparks may be small, but they are locally very hot.

Published octane ratings for a vehicle are typically the minimum octane, you can always go higher. There is an upper limit on octane where the engine simply won't run (or will run but at unacceptably reduced power output) but since fuels with that high of octane simply aren't available, manufacturers tend to ignore the upper limit. My Ducati motorcycles, however, do state an upper and lower octane limit.

 

[jetsam]

I've always used whatever Regular was in my small engines (it's gone from leaded to unleaded to unleaded with ethanol over the years) without seeing any problems.

The only engine where I've ever noticed a big difference between fuels in is my current motorcycle. I had always run premium gas in it. Tried a tank of 87 octane to see how much worse it was. Immediately started getting almost 5 MPG better mileage and slightly happier idling. I am pretty sure my old bike didn't care what kind of gas I put in it, but the new one does. (The 'new' one is a 1991 carbeurated V4, about 70k miles on it now.)

 

[Easy Livin’ 3000]

When I went to refuel one of my lawnmowers last weekend, it was half full of blue gas. I have no recollection of using the 1 gallon mix can to refuel last time (about 3 weeks ago). So I filled 'er up with straight gas and mowed away. Wasn't even smokier than usual. My concern isn't burning mix, it's that I'm losing my mind! How'd that mix get into the mower?

 

[blacktail]

When I went to refuel one of my lawnmowers last weekend, it was half full of blue gas. I have no recollection of using the 1 gallon mix can to refuel last time (about 3 weeks ago). So I filled 'er up with straight gas and mowed away. Wasn't even smokier than usual. My concern isn't burning mix, it's that I'm losing my mind! How'd that mix get into the mower?

My cheap push mower has been running on year-old 50:1 evinrude gas the last 2 years. No smoke, no problems. I wish my mower burned more gas, since it's what I use to get rid of old fuel.