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dahugo

Member
Long story short--about a gallon of mo-gas got mixed into my left wing tank so I have about a 17 to 1 mixture avgas to Mo-gas. The tank has been drained but i still have the fuel. Is that mixture diluted enough to use it in my IO-320? I just can't bear the thought of dumping $90 of fuel.
 
dahugo said:
Long story short--about a gallon of mo-gas got mixed into my left wing tank so I have about a 17 to 1 mixture avgas to Mo-gas. The tank has been drained but i still have the fuel. Is that mixture diluted enough to use it in my IO-320? I just can't bear the thought of dumping $90 of fuel.
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Assuming its alcohol free I would never have drained it, I would have just burnt it; if you were worried you could use it for cruse only and run the other tank for landing and takeoff only. Now that you drained it I would use it to top off your tank/s, which will dilute it even further.
 
I would use it!

Can't tell what you should do, but I burn pure mogas with ethanol.
I mostly use it for cruise but with only one gallon in 17 gallons of avgas
you have no concerns, ethanol or not.
You might discover the benefits of mogas. A lot of pilots on this forum have been burning mogas for years without problems.
 
I agree with Russ. I have used up to about 50% autogas (ethanol free) on one side that I used in cruise. So I would have ZERO concern with using that mixture in cruise. Perhaps no issue with take-off either but that is a guess.

If it has that ethanol contaminant in it, I cannot offer good advice.
 
dahugo said:
Long story short--about a gallon of mo-gas got mixed into my left wing tank so I have about a 17 to 1 mixture avgas to Mo-gas. The tank has been drained but i still have the fuel. Is that mixture diluted enough to use it in my IO-320? I just can't bear the thought of dumping $90 of fuel.
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I'd burn that mix in my airplane with no concerns. The octane probably meets the 100LL spec's and the ethanol content (if the mogas was 10% ethanol) is below a half percent.
 
Mogas

Many people use one tank for Mogas and utilizing it only at cruise.

The other tank is filled with avgas for take off and landing.

This has not been a problem that I have ever heard of.

Certified engines, for decades, get STC's to use Mogas exclusively.

The caution is if E10 is involved, although some use E10 too.
 
dahugo said:
Long story short--about a gallon of mo-gas got mixed into my left wing tank so I have about a 17 to 1 mixture avgas to Mo-gas. The tank has been drained but i still have the fuel. Is that mixture diluted enough to use it in my IO-320? I just can't bear the thought of dumping $90 of fuel.
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You drained the fuel because you have a gallon of mogas in it? Are you serious?
 
rocketbob said:
You drained the fuel because you have a gallon of mogas in it? Are you serious?
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My Stinson holds 40 gal of Mogas, it takes 4 hours to drain it through the drains, or 4 to drain it through the carb>engine>exhaust....guess which is more fun!
 
Rocketbob, I didn't drain it because of the mogas. I drained it completely prior to that because I was calibrating the tanks on my craft with a Dynon FlightDEK 180, and we have not had our first flight yet. DAR to arrive soon, and I don't want to do the first flight with full fuel tanks.

The drainage was really of no moment--the questions is about the inadvertant mixture of some mogas with avgas.
 
1/17 is 5.88% Mogas.
Assume as a worst case it's Regular (lowest octane) that the mogas' effective octane is only 70 in aviation octane terms. So now your mixed octane is

(16 * 100 + 1 * 70)
------------------- = 98.2 aviation octane, if you trust the assumptions.
16 + 1

What about ethanol? Assume your mogas is E15, that is, is 15% ethanol and 65% straight auto gas. Your mixed ethanol percent is

(16 * 0 + 1 * .15)
------------------ * 100 = 0.88 %
16 + 1

I think you can see why previous comments are not concerned about this.
 
A 1 to 17 mogas/avgas ratio is no big deal.

If you are really concerned just pour half into one tank, half into the other and then fill both tanks to the top with avgas.

The resulting 1 to 35 ratio is of no worry.

I you want to be even more conservative, fill one tank with 8 gallons of the mogas/avgas mix and fill to a 1 to 35 ratio while keeping the other tank pure avgas for take off and landing.

Repeat when the mixed tank is empty.

If you are filling from a plastic gas container you are probably at a greater risk of static electric sparks starting a gas tank fire than you are having a problem with the small amount of mogas in the mix.
 
dahugo said:
Rocketbob, I didn't drain it because of the mogas. I drained it completely prior to that because I was calibrating the tanks on my craft with a Dynon FlightDEK 180, and we have not had our first flight yet. DAR to arrive soon, and I don't want to do the first flight with full fuel tanks.

The drainage was really of no moment--the questions is about the inadvertant mixture of some mogas with avgas.
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ok well in that case no worries. I typically ran the other way around with no worries. :)
 
careful with the math

My old Powerplant mechanic teacher warned us about averaging octane. It doesn't work that way he said. Octane is based on a logarithmic scale, so it doesn't average. He claimed that 5 gallons of 87 octane and mixed with 5 gallons of 100 would give something like 98 octane, not 94. JMO
 
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