Auto fuel + 100LL

Salty

Salty

Touchdown! Greaser!
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Salty
So, what were to happen if you accidentally put 5 gallons of unleaded auto fuel in with 10 or 20 gallons of 100LL?

Not looking to discuss long term usage of it, but would you even notice if you inadvertently grabbed the wrong gas can one time?
 
How would you be in a situation to BUY either 100LL or E-gas? The only time I've seen MoGas offered at an FBO, right next to 100LL, it was non-ethanol.

I mix non-ethanol MoGas and 100LL all the time.
 
wilkersk said:
How would you be in a situation to BUY either 100LL or E-gas? The only time I've seen MoGas offered at an FBO, right next to 100LL, it was non-ethanol.
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I live on an airport and have a hangar on my property. I also have lawnmowers and other small gas engines on my property.
 
I wouldn't be terribly worried about it. May avoid super high power settings and super high flights until you burn it off if you are concerned. That or take some short flights and keep topping off with 100LL to dilute the auto fuel.
 
Would the OP want to add some kind of additive (Heat, isopropyl or whatever it is???) to help towards how the ethanol will change or breakdown? I thought there can be a by product of water or something if the wrong MOGAS is used.
 
Just for the record, I haven't done it. I was just looking at the sets of cans and wondering what would happen if I did. If I did it, I probably wouldn't realize it to behave differently.
 
In time the ethanol could eff up some of the rubber components in the fuel system (assuming they are the "traditional" aircraft parts and not teflon lined hoses or whatever). But it takes time so you ain't likely to notice if you only did it once.

On the other hand, the sky is going to fall, your insurance will be void, and your hair will fall out because you used an unauthorized fuel.

Oh, and I burn E-10 all the time with no problems.

And, on the other, other hand, I ain't no A&P.
 
Sinistar said:
Would the OP want to add some kind of additive (Heat, isopropyl or whatever it is???) to help towards how the ethanol will change or breakdown? I thought there can be a by product of water or something if the wrong MOGAS is used.
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I'm pretty sure the solution to having unwanted alcohol in the fuel wouldn't be to add more alcohol. The ethanol doesn't break down in the system. It can separate out from the gasoline you have too much water in the tank, but that would be an indication of a bigger problem.
 
Capt. Geoffrey Thorpe said:
I'm pretty sure the solution to having unwanted alcohol in the fuel wouldn't be to add more alcohol. The ethanol doesn't break down in the system. It can separate out from the gasoline you have too much water in the tank, but that would be an indication of a bigger problem.
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Duhh...thanks! Had water on my brain. Now its gone.
 
Tag the 100LL cans with a splash of blue spray paint.

I guess it is rocket science.
 
I usually only keep 100LL in my hangar, but with a hurricane coming I was thinking about filling the containers up with gas for the generator.
 
Salty said:
So, what were to happen if you accidentally put 5 gallons of unleaded auto fuel in with 10 or 20 gallons of 100LL?

Not looking to discuss long term usage of it, but would you even notice if you inadvertently grabbed the wrong gas can one time?
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Do you have an STC for Mogas? We burned nothing but mogas in our stc'd Cherokee for years, and I don't think anything specific was done to the engine to enable it to burn Mogas.. although if I'm wrong about that, please tell me; the STC was in place when I bought into the plane. Almost always non-ethanol, too, but on very rare occasions a few gallons of regular got added in in a pinch. Now, I burn nothing but 100LL. Got sick of lugging 5 gallon jugs, the 100LL at our airport is one of the cheapest in the area, and I've had enough people tell me that 100LL is more stable and "better" for the engine (for reasons that I don't quite get and/or haven't been really clearly articulated) that I figured what the heck.. more convenient, and possibly better. I'll take it.
 
MuseChaser said:
Do you have an STC for Mogas? We burned nothing but mogas in our stc'd Cherokee for years, and I don't think anything specific was done to the engine to enable it to burn Mogas.. although if I'm wrong about that, please tell me; the STC was in place when I bought into the plane. Almost always non-ethanol, too, but on very rare occasions a few gallons of regular got added in in a pinch. Now, I burn nothing but 100LL. Got sick of lugging 5 gallon jugs, the 100LL at our airport is one of the cheapest in the area, and I've had enough people tell me that 100LL is more stable and "better" for the engine (for reasons that I don't quite get and/or haven't been really clearly articulated) that I figured what the heck.. more convenient, and possibly better. I'll take it.
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No, and I don't want to and have no plans on burning mogas. This is NOT about long term effects, it's curiosity on the effects of mixing some one time by accident.
 
I think the biggest problem with inadvertently using gas that contains ethanol would be if you had some water in your tank. The ethanol makes instant sludge if it hits water.

BTW, this is how I test my mogas before putting it in my warrior with a mogas stc: I add mogas and water into a small jar, and shake it up. If the two separate = mogas. If I get sludge (looks like Vaseline) = ethanol.

Note: every so often, I tend to "doubt" my own ability to test the mogas, so I intentionally test some known ethanol gas. Every time: sludge!
 
Salty said:
No, and I don't want to and have no plans on burning mogas. This is NOT about long term effects, it's curiosity on the effects of mixing some one time by accident.
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Understood. I just posted because I figured that, since an unaltered (I think... again... someone jump in if I'm wrong) Lyco O-320 could be STC'd to run on pure Mogas, 100LL, or a mixture of the two, then you probably would have nothing to worry about if you threw in a couple gallons by accident once. That's all.
 
Salty said:
So, what were to happen if you accidentally put 5 gallons of unleaded auto fuel in with 10 or 20 gallons of 100LL?

Not looking to discuss long term usage of it, but would you even notice if you inadvertently grabbed the wrong gas can one time?
Click to expand...

I experienced several older cars having problems I blamed on gasahol. Leaky rubber hoses and fuel pumps. However this was over a period of several years so hundreds or even thousands of gallons. I wouldn't worry about five.
 
So, higher chance of detonation, and effects on rubber from ethanol is about it?
 
nothing.....prolly not notice a thing. It will likely run slightly cleaner with less lead.

The engine and airframe combo is not mentioned....if it "needs" 100LL it could have some knocking and detonation. Could also potentially see vapor lock if the conditions were ripe (hot temps or high alt - low pressure).
 
If you have an auto fuel STC you can mix 100LL and non-ethanol autogas all you want.

As others point out, absent the STC you have two issues: lack of octane and possible vapor lock. Had a Navion go down and pretty near killed a friend which we believe that was caused by the owner running mogas illegally.
 
Mooney with O-360. I don't think vapor lock is an issue
 
Salty said:
I usually only keep 100LL in my hangar, but with a hurricane coming I was thinking about filling the containers up with gas for the generator.
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Whats wrong with running 100LL in your generator?
 
Salty said:
Mooney with O-360. I don't think vapor lock is an issue
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Why not? This is the configuration that Petersen specifically tested and failed....

Why isn't the Mooney M-20-C or Piper Comanche approved?

The Mooney and Comanche both experienced vapor lock problems when they were tested. We solved the vapor lock problem but could not overcome pneumatic lock. Pneumatic lock takes place when the fuel boils as it enters the carburetor. The engine then dies due to an over rich mixture. This is just the opposite of a vapor lock where the engine quits or runs poorly due to a lean mixture. The better an airplane performs, the more difficult it is to get it through the flight test program.​
 
flyingron said:
Why not? This is the configuration that Petersen specifically tested and failed....

Why isn't the Mooney M-20-C or Piper Comanche approved?

The Mooney and Comanche both experienced vapor lock problems when they were tested. We solved the vapor lock problem but could not overcome pneumatic lock. Pneumatic lock takes place when the fuel boils as it enters the carburetor. The engine then dies due to an over rich mixture. This is just the opposite of a vapor lock where the engine quits or runs poorly due to a lean mixture. The better an airplane performs, the more difficult it is to get it through the flight test program.​
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Interesting, I've never seen that before. What's the source?
 
Salty said:
... I also have lawnmowers and other small gas engines on my property.
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All my small engines run on 100LL. Stays stable indefinitely. After over a year I recently started my small generator- Started on the first pull! I'd load up on 100LL. No expiration date, if not needed now, all of it can be used in the airplane, no getting any fuels mixed up.
Except for a couple bucks in extra cost, no downside.
All my portable jugs are nothing but 100LL.
 
Salty said:
So, what were to happen if you accidentally put 5 gallons of unleaded auto fuel in with 10 or 20 gallons of 100LL?

Not looking to discuss long term usage of it, but would you even notice if you inadvertently grabbed the wrong gas can one time?
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If you put 5 gallons of unleaded with 10% ethanol into a 20 gallon tank and topped it off with 100LL, the alcohol content would be 2.5% and the octane would be >90.
 
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Salty said:
I live on an airport and have a hangar on my property. I also have lawnmowers and other small gas engines on my property.
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I run all my small gas engines on premium mogas with zero ethanol. They don't seem to do well with that corn mash shzt.

If the inadvertent fuel contains ethanol I would drain it immediately out of my airplane. All of it.

I would do the same if the plane has high compression pistons (e.g. an engine that cannot be mogas approved).

To the original question (assuming no ethanol), "the solution to pollution is dilution", so 5 gallons adequately diluted with a full tank (40, 50 or more gallons) of 100LL will probably not make a great deal of difference in a low compression engine. But I would probably be prudent and run ROP and perhaps limit the max power setting while I burned it off.
 
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Watch your octane rating. If there are mogas STCs for a given engine, then you’re fine. If there are not, then that engine may not be able to handle octane rating less than 100.

The end result might be detonation. Detonation can lead to catastrophic engine failure. I try not to exaggerate on the internet, cuz guys will jump my ****, but in this case, it’s a big deal (to me).

The octane math is normally pretty simple, just a ratio, but mogas octane and avgas octane are figured differently, so you’re not going to get a simple answer. Gotta be able to determine the avgas equivalent octane rating of mogas to be able to do that first, then calculate.

Road gas (RON+MON)/2 Octane numbers mixing example:
5 gal of 87 + 5 gal of 92 = 10 gal 89.5
 
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MuseChaser said:
Understood. I just posted because I figured that, since an unaltered (I think... again... someone jump in if I'm wrong) Lyco O-320 could be STC'd to run on pure Mogas, 100LL, or a mixture of the two, then you probably would have nothing to worry about if you threw in a couple gallons by accident once. That's all.
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Read the fine print in the STC. It forbids ethanol.
 
Mixing TEL into unleaded gas has a pretty non-linear effect - the first little bit gives a significant boost to octane,then it becomes less effective as you add more. Trying to figure out the octane by just calculating the ratio of auto and 100LL fuel isn't going to work.
The reason for not getting the auto fuel STC (at least what was posted above) was not an issue with octane and detention. It was an issue with vapor pressure under some circumstances. Running on straight auto fuel would be one thing, but 20% or less auto fuel is not going to be nearly as bad. (Not that I am recommending a regular diet of auto fuel in this case...)
 
Non Compos Mentis said:
All my small engines run on 100LL. Stays stable indefinitely. After over a year I recently started my small generator- Started on the first pull! I'd load up on 100LL. No expiration date, if not needed now, all of it can be used in the airplane, no getting any fuels mixed up.
Except for a couple bucks in extra cost, no downside.
All my portable jugs are nothing but 100LL.
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:yeahthat:
Just be sure not to put it in your modern car...
 
It's probably no big deal, but personally, I'd drain it and burn it in the lawnmower. I have no idea what effect ethanol might have on the seals in the fuel system, and I'd rather not find out at altitude.

When I pump ethanol-free for any purpose aviation-related or otherwise, I fill up my car first to make sure I get past whatever the last guy to use the pump left in the hose. I know the car can deal with up to 10 percent corn. I'm not too sure about the fuel system of an old tractor or an aircraft engine that expressly forbids ethanol.

The slightly-reduced octane is also problematic. It could cause detonation. Running just a tad on the rich side might be advisable.

Rich
 
Between the farm, the yard and the hangar, I have need for all kinds of different fuels. I have 20 red (5) gallon gas cans and (6) blue* diesel cans.

I don't permanently tag the gas cans, that would be too limiting. I use surveyor's flagging tape tied around the spout.

Red = E10
Green = E0
Blue = 100LL (duh)
Yellow = sta-bil added ... always used in addition to another color, typically E0.
White = two stroke oil added.

No tag = fell off...so it goes into lawn/farm equipment.

Been doing it this way for 15...20 years. Works well, quickly ID. I can count on one hand how many times the can lost flagging.

841209D8-E331-4D1D-95E2-33208E3A0DAE.jpeg

*blue cans are actually labeled "kerosene," yellow are for diesel, but yellow cans get stained and nasty looking very quickly so I've always used blue for diesel...
 
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