Rotax fuel

MMorgan

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I know this has been discussed and I searched all threads in the engine section but did not see it.

I would like to run 100LL in my 618 since it is very convenient at the airport and the price now is only 25 cents more than premium unleaded.(We have our own fuel farm and get 100LL about a dollar less than most FBO's)

I know all the problems it causes in low compression 80-87 aircraft engines, mostly valve related, but the rotax is much different.

Anyone out there used it for a long enough time to have some history to report??
 

GyroRon

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Mike, I know people will disagree, but I use mostly 87 Octance autogas in my Rotax ships and have not had any problems.
 

JoeSwanton

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Mike,

It will run fine on 100LL and many people prefer to use it all the time. If you plan to strictly follow the Rotax manual for time between teardowns it is great fuel for the Rotax. However, on my personal single place gyro I don't want to tear it down that often (and I'm a mechanic for a living) so, I always burn Amoco Ultimate 93 octane car gas. Ultimate will not leave the harmfull lead deposits on your pistons the way 100LL does after extended use.
When flying cross-country I use 100LL because that is usually all thats available, but I never use it if I have the option to use Amoco Ultimate. In my two-place trainer I tear the engine down every year anyhow , but I still try not to burn any more 100LL than I have to. The incomplete burn of the fuel in a 2-stroke is the real issue, leaving the deposits to build up over time. Now in a 4-stroke engine I would say 100LL is one of the most reliable fuels available. To me it's not about the cost of one fuel over another but what my past experience has shown me happens inside the engine. These are just my opinions however and it is up to you to decide for yourself
 

JoeSwanton

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Ron,

Most people that use high octane gas in their cars are indeed pissing away money because the modern engines with electronics don't need it. Only high compression, high performance engines really need the high octane.
The octane rating is a measure of how resistant the gas is to self ignition under compression. lower octane gas with high combustion chamber temperatures can more easily expierience pre-ignition which can very quickly spike temperatures to catastrophic levels in a 2-stroke. Higher octane gas is less likely to let pre-ignition take place.
Interestingly, lower octane gas burns faster, so in the short power stroke of the 2-cycle engine a lower octane gas gives slightly more power (which makes more heat). can you see the snow ball effect that could get started here?
Personaly, I would rather spend a little more for the higher octane gas for my flying in order to eliminate the chances of pre-ignition even if it makes slightly less power.
Also, There is are lot of engine problems blamed on BAD oil, but oil is only 2% of what we are feeding these engines. 98% of their diet is the gas we choose. The cost savings at the pump is not worth it to me.
 

GyroRon

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My temps - CHT and EGT and Water Temp - do not change more than a few degrees + or - when I go from 93 Octane to 87 or back to 93. I hear no bad sounds, and have not seen any more build up of carbon etc...

93 octane costs about 20-25 cents more than 87 octane around here. 93 is now over 2.25$ so there is a difference in price that adds up. I typically fill up 4-5 Five gallon jugs at one time so using 87 saves me enough money to buy lunch or 2 quarts of oil....

I just see so many people that don't understand fuel that act like the higher the octane the better the fuel is, and since this is a aircraft engine it would be foolish not to use the best. I just don't think if the engine doesn't need it, it isn't exactly better for it. Same thing with certain 2 cycle oils, I know some people out there are spending 2-4 times as much on oil as I am and I know they are just pissing away that money for a warm fuzzy feeling that does nothing performance or longegivity wise.

And yes Steven, alot of modern performance cars do require 93 octance, they have the high compression pistons and advanced timing to make as much power as possible. If you use low octane fuel the engine will detect the lower grade fuel and retard the timing, which saves the engine from getting hurt but also makes less power than it would normally make.

IMHO if the car requires it, or the aircraft engine requires it then it is a good idea to use whatever they suggest. All my vehicles and equipment except my Airplane only require 87 Octane including my rotax on the gyro. The plane I am not sure about... it has a 160 horsepower lycoming and who would think it needs avgas, but I am searching to see if there is a STC for autofuel that applies for that engine.
 

MMorgan

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Hey Ron....just use unleaded plus...seems like a good compromise.

Your 160 hp engine should be stamped on the data plate as a 91/96 octane engine. I used premium in these engines for years with no problem. Not sure now if there is an STC ( I didn't take the time to search) but I think there is. Same for the 180 hp Lycoming...it is a 91/96 octane motor. I flew my Beech Travel Air on auto fuel for years and it had two 180 hp Lycomings. Also flew my Aztec on auto fuel with two Lycoming 0-540's at 250 hp each....again 91/96 octane engines.

Do not put auto gas in any engine that is stamped 100/130 octane....unless, of course, you are the highly modified gyrobee builder in Idaho.
 

GyroRon

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MMorgan said:
Hey Ron....just use unleaded plus...seems like a good compromise.

Your 160 hp engine should be stamped on the data plate as a 91/96 octane engine. I used premium in these engines for years with no problem. Not sure now if there is an STC ( I didn't take the time to search) but I think there is. Same for the 180 hp Lycoming...it is a 91/96 octane motor. I flew my Beech Travel Air on auto fuel for years and it had two 180 hp Lycomings. Also flew my Aztec on auto fuel with two Lycoming 0-540's at 250 hp each....again 91/96 octane engines.

Do not put auto gas in any engine that is stamped 100/130 octane....unless, of course, you are the highly modified gyrobee builder in Idaho.
I liked that funny part at the bottom!!!
 

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MMorgan

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Does that mean you did not care for my first line suggestion???

My 618 manuel says to use MON 85 or RON 95 fuel which I believe is Motor Octane and Research Octane numbers. Gas station octane numbers posted on the pumps are an average of these two numbers last time I noticed.

Therefore I would assume that 90 octane is the min that should be used....which would seem to dictate the use of premium or at least the plus which is usually posted as 89 octane.
 

GyroRon

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Use what you think you should use.... I have used 93 for years and then switched to 87 for about the last 4 years or so. Didn't notice any changes. I guess 89 would be a good middle ground, but if the engine is running good on 87, CHT and EGT and water temps are in the right range and carbon build up is typical, why spend another dime a gallon if you don't need to?

Of course that just shows how much of a cheapass I am! ;) I flew this afternoon for 1 hour 28 minutes and burned exactly 4 gallons of gas.

I will probably go back to using 93 in it since I was told by not only you, but another person I trust as well, to use at least 93 in the Lycoming and since I use the same jugs to fill up either ship It will be easier to just have 93 in all my jugs.
 
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