40:1 or 50:1 two-stroke tools (what to do if you have both)?

[jamesgangnc]

The ratio depends more on the oil than it does the equipment. I run everything I have on marine 2 stroke oil at 50:1. We have a jetski so we buy oil by the gallon. I've been doing it fo years and haven't had a problem. My chainsaw is 30 years old. I've got a lawnboy that is

20 years old.

[Steve Barker]

Your thinking is correct. the reason they recommend the higher octane is solely the compression ratios.

[Steve Barker]

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I also ran about 50 gallons a week of 50:1 mix gas through about 30 pieces of equipment, for almost 2 years. (That's a lot of gas and oil) Using only quicksilver oil mix. THEN the stihl guy caught wind of it and advised us that any lubrication based warranty claims we might have could be denied, so i switched to the stihl oil.

[jamesgangnc]

Th stihl guy is lying to you. There are consumer protection laws that prevent any manufacturer from voiding a warranty claim as long as you have used oil that meets or exceeds the equipment requirement. No matter who made the oil. You can use the walmart oil and they can't do a thing about it.

[Steve Barker]

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That's true, but the merc quicksilver oil is certified for water cooled. I doubt it meets the requirements for the air cooled spec.

[clare]

Absolutely sure - and I'm likely one in a thousand on this group that actually understands octane and detonation in an internal combustion engine.

Octane of a fuel has NOTHING to do with how fast it burns - and if it did, FASTER burning fuel would have a higher AKI or octane rating. This is because of the way detonation happens - unburned fuel - endgasses - in the cyl dissassociate into hydrogen and oxygen radicals, which are extremey active and explosive. This only happens with temerature and pressure over time - so if the fuel burns FAST there is less endgas in the cyl, for a shorter time - so less chance of disassociation and detonation. (also part of the reason an engine knocks more at low speed than at high speed, generally speaking.

This is a very "dumbed down" explanation - but it is accurate as far as it goes.

[clare]

4 out of 5 of those references are accurate. The one that is not is the one from Bubba the BassFisher.

As far as the one about not using more than recommended, it is only accurate if using the correct oil. If NOT using the correct oil, more oil may provide close to the same protection as using the right amount of the right oil. - but it IS true.

As for not using synthetic 2 stroke oil, it is also accurate - particularly with a simple port timed 2 stroke. A rotary valve or Rave valve 2 stroke is more of a sealed system when shut down, suffering less from moisture and corrosion issues - the ideal may be to use a semi synthetic - just enough "real" oil to provide some anti-corrosion protection, while most of the lubrication is provided by the "smokeless" synthetic.

On a $99 weedeater I wouldnt worry too much about it, but on an $8000 Rotax aircraft engine Iwould pay heed to their warnings.

The problem with Bubba the Bassfisher's assertion that oil increases the octane rating is that it is just plane WRONG (hey, don't take my word for it - Echo, and Rotax - MAJOR manufacturers of 2 stroke engines agree)

[clare]

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But using oil for a water cooled 2 stroke in a highly stressed air cooled engine is NOT recommended (generally) and MAY require a different mixture. Some, but not all "outboard motor oil" is suitable and meets the JASO M345 FD spec. If it only meets tc/w3 it is not recommended for, for instance, chain saw use. JASO M345 Fd severely limits engine deposits and reduces smoke, as well as requiring minimum lubricity levels etc.

[clare]

No, it is not correct. Oil reduces the AKI of a fuel. And if you read to the bottom of the bassfisher blog you would see that the error was corrected.

[clare]

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True - as long as it meets or excedes the published spec. If it does not, and they can prove it - you have no warranty.

[SF Man]

The Bruce Hamilton gasoline FAQ covers octane ratings in detail:

Unfortunately, Bruce didn't add a question to the FAQ of:

- Does adding 2-stroke oil to gasoline raise or lower the octane rating?

So, I will send him an email asking him to include that in the next revision of the Gasoline FAQ so that we may all benefit.

If he provides an answer via email, I'll post it here.

[SF Man]

Still googling, I find this which backs you up:

"When all of the two strokes (the old days) were developed, they all used Castrol petroleum oil at a 20:1 ratio and found that 92 octane gas had the octane reduced to 72 with presence of that much oil. Modern oils wonÿt affect the fuel quite as much, but if you started with 86 or 87 octane regular fuel, you can see where youÿll end with a very low octane mix. You could end up with a ´pinging¡ bike."

[zxcvbob]

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Look at the Quicksilver PWC oil. It is certified for air-cooled and not water cooled. It's expensive; I think it's about $9 a quart at Walmart. I haven't bought it because I'm still working on a bottle of Castrol

2-cycle oil.

-Bob

[Bubba]

replying to Steve Barker, Bubba wrote: It wont hurt using ONE tank that much. Using fuel that isn't the same ratio will harm the unit. It will carbon up and rings will stick, exhaust will get clogged and the combustion chamber will be full of carbon. 35 years as a factory tech for stihl( gold) ,echo, husqvarna and a master OPE TECH.

Not a good idea.

[Bubba]

replying to zxcvbob, Bubba wrote: And you would burn it up with a leaner mix...you garage mecahnics are what keeps me fed...but don't tell folks stuff that ruins their equipment.

[Bubba]

replying to Jules Richardson, Bubba wrote: You will burn up it up with your thinking.....its not designed to run with 'close enough' ratio fuel mix. Don't understand why folks want to shortcut stuff ...then it tears up. Then you bring it to me for warranty, and I know that you haven't used the right ratio , when I go through it, and I tell you too bad, and then you get mad. Be smart , not lazy. It will save you time nd aggravation.

[Bubba]

replying to Tony Hwang, Bubba wrote: And you will cause a carbon to build up...when it breaks loose it will devistate the engine ..not smart advice.

[Bubba]

replying to clare, Bubba wrote: Correct! Finally someone with sense...

[Bubba]

replying to Ed Pawlowski, Bubba wrote: Fouled plug is the least of your worries...carbon build up in the chamber, rings, and exhaust port....when that carbon breaks loose, it devistates the cylinder and piston...you're givem incorrect advice. Smh

[Bubba]

replying to SF Man, Bubba wrote: Thank you for posting. It drives us techs crazy when people use the advice of people who don't research. Its refreshing.