Aviation Gas for Long Term Storage?

W

woodburnranch

Senior Member
I have some vehicles destined for and already into long term storage. I have an additive (not Sta-bil) that has worked well with non-ethynol gas in older trucks that just move a little seed around the farm and haven't had fresh fuel in years. However, my brother just purchased an old Diamond T truck from a neighbor that has 10 year old aviation gas in it with no fuel related problems and I'm thinking that may be a better option. I have a retired chemical engineer friend that is into moto-cross racing and he told me that his friends that went to av gas in their two-cycle motorcycles for higher octane burnt up the engines because av gas burns hotter than normal gas. Does anyone know if this higher combustion temperature would be an issue in older carburetor and/or newer fuel-injected automotive engines? Is there any other disadvantage of using av gas?
 
When I was a kid we used to ride our Honda 305 scramblers to Flying Cloud airport to fill em with AV gas. Big power we thought. Go like crazy... guaranteed .0001 Hp increase!

I'm not the expert here, Rotorwrench will chime in with some facts, but its basically non alcky, high octane. High octane is good for pinging issues on high compression motors, but really has nothing to do with storage.
 
Not a chemical engineer but I keep my ears open, so this is what I have heard and read: Av gas is high octane without ethanol. Ethanol is high octane without lead. High octane is slow burning, which provides power through the power stroke rather than a quick bang at the beginning of the power stroke.
Both lead and ethanol have bad reputations, but lead has enough going for it to be considered a safer fuel for planes up there in the clouds. One of ethanol’s problems is that it attracts moisture. Lots of moisture. The best known fix for that is to isolate it from contact with air, which provides that moisture.
One product I know of that does that nicely is Stabil Marine. It has an oil base that floats on top of the ethanol, thereby separating it from contact with air.
Now to answer about two stroke engines running Av gas, I can’t picture someone running straight Av gas in a two cycle without an oil additive, but just maybe that actually happened.
 
Nothing good will happen by by burning higher octane than an engine was designed for or modified for. It is essentially harder to ignite in the sense that it can withstand higher temps and compression before igniting. Burning in a lower compression engine leads to unburned fuel and carbon build up.
 
it's my understanding that AV gas has lead in it, has a very high octane (100+) rating and has no ethanol. some would argue that ethanol in gasoline is a problem if left in carburetors and gas lines and tanks for long intervals. i have no first hand knowledge of that but i wouldn't be surprised if it did.
 
Having an insufficient amount of knowledge about the subject, I don't have any credible
comments to make so I'm currently waiting for someone to chime in and offer credible
evidence about the pros and cons of going in either direction. I've used both AV gas and
ethanol gas in my Model B and 36 V8 and don't have any memory of either one of them
running worse or better from either fuel. However, I haven't been a fan of ethanol gas
sitting in my tanks for extended periods of time so chose AV gas for that reason.
 
Not too sure what the op meant by “long term” but I have used pump gas in the ’49 since we bought the car 40 years ago and have stored it for 6-10 months many times. Never had an issue but I was anal about a clean tank, 30R7 hoses, and ethanol friendly carb and fuel pump parts.

Yes, I did use Stabil during those times simply because I was servicing the boat also. Takes 2 minutes to dump in the required amount and drive it around the block. The way Stabil works isn’t going to cure your ethanol problems if you don’t have ethanol friendly parts in your fuel system.
For the trophy hunters who must run NOS/script hoses etc, ya you are gonna have problems.

About Avgas, I grew up in the era where avgas was rumored to be the holy grail/cure-all and double your horsepower to boot. Jeez, we were gullible back then. Most avgas now days is LL (low lead) with a chemical stew to help boost octane.
 
Ethanol is hygroscopic. It can absorb moisture from the air. Because ethanol blends readily with water, gasoline that contains ethanol is generally more prone to taking up moisture than pure gasoline.
With that being said. AV GAS does not contain any ethanol and is not prone to absorbing moisture. Less moisture = less corrosion.
The 100-octane low lead fuel does contain traces of lead, but should not be an issue if only one tank / per year is ran through your engine.
I used to be into experimental aircraft and most of the engines we used required MOGAS (regular fuel from a gas station). Most of the airports we flew into did not have MOGAS so we would use AVGAS to get us back to our home airport. Even in the aviation world, using an occational tank of AVGAS was not an issue.
 
The most common available avgas is 100 LL or Low Lead blue color. It still has enough tetra ethyl lead or TEL to give it the 100 octane level. 80/87 red avgas is not near as common & near impossible to get so some get the STC to blend a ratio of 87 unleaded alcohol free Mogas to 100LL to reduce the octane for their old low compression engines like the Contenintal A65 and others of similar compression ratio. The helicopter engines that I worked on a lot were 11:1 compression ratio and originally used 100/130 green avgas but the 100LL will work just fine in those engines. The 115/145 purple avgas was used in the warbirds of old but is no longer available to general users. The warbird comunity has to get together and spend some big bucks to get that stuff blended and I'm sure it ain't cheap. Engines like the Merlin and the big bomber engines still have to use that stuff just due to the huge size of their pistons and valves.

In summary, avgas is not really any advantage in smaller engines. It tends to lead foul the spark plugs plus it's expense is just not worth it. High octane racing fuels are preferred in the modern era over any of the avgas types for those that race with it. This type fuel and the ag type diesel fuel are not legal for use on the american roads. Here in Texas, we have fuel police in the agricultural communities that stop farmers now and then and actually take a sample from their fuel system to make sure that big tank of tractor fuel isn't in their pickup truck. You may think I'm joking but it's no joke if you get caught. The fines are high for those found breaking the rules. They also catch youngsters that steal fuel out of parked tractors. They have it down to a science. I would recommend finding a local source for mogas with no ethanol in it. That's what I use for my tractor and lawn equipment. I have several local sources for it but it is more expensive.
 
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Avgas will not go bad nearly as quickly as Mogas will. We never worried about bad gas even if the aircraft engine hadn't been run for 3 years or more. But, having dealt with avgas that had been in an unused drop tank for over 20 years I do know it will go bad eventually.

If you don't need the octane it's not worth the trouble. You won't gain any horsepower using it.
 
What do you mean by long term storage. If longer than 6 months maybe a you should drain all the gas out of the system - tank, carb bowl, etc.
 
Most of us around these parts put their internal combustion engines away with the expensive chain saw mix from Stihl or better yet the generic stuff from the ace hardware store as it's half the price. It's 50:1 with the 2 stroke oil, non ethanol and I guess rather high octane, and it leaves no residue whatsoever in the carb or tank in the spring. Let's face it, somehow a 2 stroke engine oils it's mains and rods with a touch of oil in it's gas. No clue how that can be...That same oil should help out our valve stems and our needle/seat in the carb while they are hibernating for the winter.
 
If we are getting on the subject of winter storage, I'll chip in my two cents. I always figured that if the gas was gonna absorb anything, it will come from any air left in the tank. Every winter, before I went to Florida, I would fill each car with gas, trying to get as much in as I could (rocking the car during the final gallon or two). I would put in a pint of SeaFoam (Sta-Bil is too expensive) before filling so it got mixed in. I would then drive the short distance back to my shop. When I got there, I would put the car away, and the last thing before covering, I would carefully fill the tank from a 2 gallon can of gas I had. This way, there was almost no air in the tank over the winter. It was a lot of fooling around, but over 25 years with as many as 5 cars, I never had a problem with gas.

I also had maintainers on all of the batteries. In addition, the maintainers were plugged into mechanical timers that were set to run 15 minutes twice a day. This way, if a maintainer "ran away" (I've had it happen), it wouldn't "boil" the battery and ruin it.
 
AV gas will work in A's just fine, and is a great fuel for these cars, no matter how long they sit. The advantage is, it does not contain ethanol. Run it if it's convenient to obtain.
 
Just curious. I access to both AV gas as well as Ethanol free gas from a station near me. Is one better than another of am I just making to much of this?
 
The ethanol free gas sold at gas stations is legal to run on the road. Avgas is not legal but the fuel police don't look for it. They are only concerned with diesel fueled vehicles. The local ethanol free mogas is 90 octane so it's a pretty good blend.

On occasion, the aircraft I maintained would set for long periods due to owner inactivity for one reason or another. I always drained about half of it off and mixed into other aircraft so as not to let it go rancid. The blue die would start to settle out of it over time and a person could tell it was starting to go bad. We would then refill the aircraft with fresh fuel to go out and fly it for test run after the annual inspection completion. I wouldn't use any fuel if it set over a year without at least mixing it with half again the normal quantity before flight. A person should really de-fuel an aircraft and follow the system preservation procedure if it's going to set more than 60 days. This is the way we did it in the military but we generally ran it up every 14-days as a maintenance operational check. The civilian world doesn't follow those rules very well.
 
For long term storage I empty the tank and run the carbs dry and then put in VP racing 50:1 fuel and the appropriate amount of sta-bil fuel stabilizer. The VP is ethanol free and can sit for a year without issue, and the oil in the mix helps keep the internals lubricated. And I believe it is 97 octane.
 
The guys with outboard motors always run Startron fuel stabilizer. I switched to that from Sta-bil and the results were dramatic:)


I only use Startron and only run no-ethanol gas. We can get that from Phillips 66,Conoco, and Mobil/Chevron stations around here. Also a shot of MMO.
 
I am surely enjoying this discussion as I do most. I am no chemist at all. I can say when storing way too long as seems lots of us do there is no comparison to what is left as the results of evaporation and deterioration. I wont get into the brands of additives I have used over the years, but will say I use nothing but ethanol free fuel with the additives and as I said before left setting way too long the results is nasty. With av or racing fuel when left way too long (with less than 1/2 tank each time) the results are just a light powdery reside after it evaporated an no nasty stale fuel left overs. I agree with all the comments on this subject, and know the bottom line killer for fuel is setting too long. Everyone take care. Steve
 
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