Backcountry Pilot • Autofuel VS avgas

Autofuel VS avgas

Nothing happens without it. Discuss fuel locations, quality, alternatives, and anything else related to this critical resource.
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Autofuel VS avgas

This has been beat to death I know.........but my horse is still kickin.
I ask other pilots what their thoughts are and half of them say don't do it, you are asking for trouble......detonation, vapor lock, deteriorating gaskets, the risk of ethanol, the list go on and on.
The other half (which uses it) say it is better for our low compression engines, no fouled plugs, no valve erosion, cheaper, and again the list goes on and on.
I burned 100ll in the 165 Franklin, leaned it aggressively.....stuck one valve and had problems with fouled plugs. TCP added to the 100ll seemed to end the lead problems, but it is nasty stuff and expensive.
I have 100+ hrs in the O470 with auto fuel and it seems happy. I add 2 or 3ozs of MMO per 10gal of gas, mostly because I think it will help my fuel bladders.
Last month I saved about $1.25 per gallon using auto fuel, doing the math at 13gph, in 1000hrs I will have saved $16250. If I make TBO the savings will buy my next motor.
I have yet to here anyone say auto fuel ruined my engine.
Does anyone on here have actual experience with using auto fuel and think it will lower the TBO on an engine?
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Re: Autofuel VS avgas

I'd sure like to know the real answer cause I'm told that it will "ruin" my IO-390 ...
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Re: Autofuel VS avgas

We use auto fuel in the 7AC Champ...65 hp motor, without any overt problems, but I can't say wether it shortens engine life or not. One problem I experience in my motorcycle is that if I let it sit for a while, the auto fuel will separate. That is a huge head ache requiring draining the fuel and cleaning the carb (disassembly). If I had a plane that spent anytime not flying, say a month at a time, I wouldn't use ethanol blend fuel.
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Re: Autofuel VS avgas

I used autofuel in my Ercoupe for a while (C-85 engine). The only difference I noticed was it used 1/2 gallon per hour more than 80 octane on cross country flights. I stopped using it when I got some bad fuel and couldn't get enough speed to get off the ground from a 3600 foot strip until I drained the tanks and refilled them with different fuel.
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Re: Autofuel VS avgas

I've used auto fuel for at least 1,000 hours in two planes; a C-182 (O-470) and now an experimental Bearhawk (O-540) with no issues. I have never had any performance differences using non-alcohol tainted fuel. The gas station right next to the airport sells ethanol-free gas so it is pretty convenient for me to use. A 50 gal transfer tank in the back of the truck is used to cart fuel to the airport and a set of 4 metal 5gal cans is kept handy for back up. Testing for alcohol in fuel is simple and easy, so it is recommended if you are uncertain. A fuel filter is used on the discharge-end of the transfer pump and a Mr. Funnel is used as a filter when fueling from cans.

I spend a lot less time cleaning spark plugs now than on pure 100LL. If I'm not flying for more than a month or so, a fuel stabilizer is added to ensure the auto fuel won't go bad in the plane.

Auto fuel is lower octane than 100LL so it is not suitable for high-compression engines like the IO-390. However, if an auto fuel STC exists for your plane/engine or if experimental, a low compression engine (need to also be sure components in the fuel system are compatible for auto fuel use); go for it and don't look back.
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Re: Autofuel VS avgas

I think that the engine damage concerns you frequently hear regarding use of auto fuel are mostly overblown. Granted, if you are running an engine with high compression, that requires a high octane rating, detonation is a significant concern, but most of our little engines, and certainly the O-470, are pretty low compression.

The thing I WOULD be concerned with is the additives in gasoline and their effects on the rubber parts in my airplane. And, there are quite a few rubber parts in most airplane's fuel systems. Most of those are pretty small, inexpensive and relatively easy to replace.

If I had an airplane with fuel bladders, there is NO WAY I would run auto fuel in it. That fuel is sitting those bladders 24/7 and the additives in that fuel (even non oxygenated fuels) WILL attack the materials in those bladders. First time you have to replace a bladder all that fuel savings will be long gone.

But, an airplane with hard tanks....I have and would again run some auto fuel, well filtered and ONLY non-oxygenated.

MTV
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Re: Autofuel VS avgas

Yeah, the premium auto fuel ruined my cousins 182 bladders in only 10+ years of use. Of course they were quite a bit more than 10+ years old when he bought the airplane......, so, let me see...... What is life expectancy on those things, anyway?

lc
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Re: Autofuel VS avgas

I had the opportunity to run it in my cub a couple of times, the airplane didn't seem to know the difference. It did smell bad, in my opinion.

Had the engine overhauled (C90-8) by John Alsworth at Alaska Aircraft Engines. His advice was NOT to run MOGAS as it didn't provide adequate cylinder cooling tjat resulted in several cases of premature cylinder failure in his experience.

I have a friend that ran it in a C182. After multiple carb issues he has gone back to AVGAS with no further problem. This could easily be our fuel source and the lack of filtering.

If it works for you then go for it.

GB
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Re: Autofuel VS avgas

I ran it in my PA-22 with zero problems for a few hundred hours. I filtered it through a chamois. Cylinders and carb stayed clean.

I was absolutely convinced there was an issue with the brand of fuel though. The Conoco gas in the 80's in Grand Junction appeared to make less HP (lower climb, a few mph slower, RPM on climb out definitely very slightly lower). I suspected it for about a year before I actually tested it for several hours over a couple weeks, using just enough fuel to tool around for an hour while taking notes on performance, then filling up to dilute the few remaining gallons, burning down to minimums again, taking notes, repeat...

The Conoco fuel at the time appeared to produce less horsepower than the Amoco or the Sinclair. The Amoco and Sinclair gave numbers that were tough to tell from 100LL. The climb rate on Conoco gas seemed to suffer by as much as 50 fpm (given that my regular climb rate was around 400 fpm, it was something to ponder: >10% difference). The Conoco gas came from a single refinery. The Amoco gas came from a local blender. The Sinclair gas came from their refinery. Same octane ratings.

It wasn't scientific, but I think it might be more than anecdotal. Just be aware there *might* be more variation in energy per volume with automotive fuels than avgas. I never really cared about the variation except on hot days where I was struggling at 250-300 fpm, when 50 fpm really starts to mean something. I also had an experience with auto gas out of S. Idaho that had my prop turning *faster* than red-line on climb out, at an altitude comparable to when I did my own private test. It only happened once, and I think that could mean either there was something else in the fuel to make the engine produce a bit more power or the RPM gauge picked a single day to be different.
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Re: Autofuel VS avgas

My experience was good with auto fuel I used to do a 50/50 mix with no negative affects.

Must be a short wing thing because I too noticed reduced power in my 22 with straight auto fuel. But I think it has more to do with the quality of fuel rather than the short wings.

It was weird it seemed whenever the gas prices were on the rise the auto fuel performed even worse I suspected some of the places I was getting my fuel they were cutting the fuel with something to increase their profit margin so I switched back to straight 100LL.

I've heard of gas stations doing this but not sure if its actually a real thing or not, I guess if you had a trustworthy supplier or a bulk plant you could get the fuel from you would have no problems.

B
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Re: Autofuel VS avgas

The Conoco fuel at the time appeared to produce less horsepower than the Amoco or the Sinclair. The Amoco and Sinclair gave numbers that were tough to tell from 100LL. The climb rate on Conoco gas seemed to suffer by as much as 50 fpm (given that my regular climb rate was around 400 fpm, it was something to ponder: >10% difference). The Conoco gas came from a single refinery. The Amoco gas came from a local blender. The Sinclair gas came from their refinery. Same octane ratings.
Thanks for posting. You made good point about what might be going on with fuel today.
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Re: Autofuel VS avgas

I used it in my F 19 Continental o200 four right at 1000 hours with no problems and continue to use it in my F 22. lyc o235

I think the biggest thing and most important thing about using car gas is that you have to fly on a regular basis and if you don't that's where the problems come in. Mechanic has pretty much told me at every annual my spark plugs are good as new.

The one drawback is that you are definitely more susceptible to carburetor icing when using car gas not sure why but there is definitely a noticeable difference.

One other note on the topic of gas and alcohol, father-in-law told me about the product star Tron fuel additive does anybody have any experience with it as far as lawnmower motorcycles etc. not putting it in my plane of course just curious
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Re: Autofuel VS avgas

product star Tron

I think you mean Startron. My bro in law adds it to the E10/two cycle oil mix in the boat motors. One boat has two 175 hp Mercury's. I don't know if it really does anything but it doesn't hurt. The boats might sit in the Chesapeake Bay for a few weeks without running and he hasn't had any trouble.
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Re: Autofuel VS avgas

Stations have been known to sell 'premium' fuel cut with 'regular' to make (addnl) profit on their fueling operation. A lot of stations make a LOT more profit on the 'mini-market' goodies-pop, candy and such-than they do on their fuel sales. On fuel the margins are/can be pretty thin.

This reminds me of a (true?) story in more innocent times back in the days when the 'majors' (oil co) owned everything up and down the supply line and the individual station owners were getting squeezed awfully hard to survive-well before 'mini-markets' came along. All they had was fuel and their grease rack to turn a living.
A station in a small town on a main 2 lane highway with one each of the 'major brand' stations was suffering an inspection by the regional manager. When he came out of the ladies restroom he was livid. "You take that rubber machine out of the ladies bathroom-right NOW! We don't run that kind of place!" To which the owner protested "That would put me out of business! That is the ONLY money I make in the whole place!" The RM got an astonished look on his face and said "You sell that many?"..... The owner got red and squirmed a bit and said "That machine has NEVER had a rubber in it-so I'm not 'that kind' of place. And before you say anything about that, I have not EVER had even one complaint!"

Having a tough time making a living is certainly NOT unique to our times.....
It is more the 'norm'.
lc
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Re: Autofuel VS avgas

ya my typo
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Re: Autofuel VS avgas

I love Mogas BUT! My Maule has the B4B5 low compression engine. If I remember correctly, only the Lycoming B4B5 has a STC. Other models have to high of compression. My Maule has the Peterson STC. The STC is more than just a sticker.

On mine it includes different fuel pump system. The stock engine driven pump, an electric pump operated by the pilot, a second electric pump operates when ever the master is on.

One additional scat tube takes air to the engine driven fuel pump and a scoop, to the gascolator.

Instructions on how to operate the system, particular detail if you experience vapor lock. Instructions on how to test for ethanol. Ethanol not allowed! I can use 87 but I don't. Only premium!

I have never had a vapor lock issue. Zero.

When we overhauled the engine, zero issues from mogas.

If you run mogas with no STC that makes you a test pilot, EH!

Good day
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Re: Autofuel VS avgas

I've been running car gas for the last 16 years in an O-200, an O-300, and now an O-320. No problems attribuable to the fuel, in fact quite the opposite-- clean plugs every year at annual time and no stuck valves. I started out running 75% car gas/ 25% 100LL, but for the past several years I've just run straight car gas, except on trips when I couldn't get any. Always ran 87 octane regular, but the only local E-zero is 92 octane premium so that's what I use now. Only thing to watch out for with the low compression engines is not to bump the timing up for more power-- you can get away with that with 100LL but I wouldn't try it with 87 or even 92.
Even paying an inflated price for the E-zero stuff, it's still over a buck & a half cheaper than 100LL- at 8.5 gph that's $13-15 per hour savings. Like Terry, I'll have saved enough money by TBO to pay for the overhaul (and then some).
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Re: Autofuel VS avgas

I'm talking about E0 fuel here. If you leave it in for a long time there are some problems with it. The newer fuel will attract water whereas the older fuel wouldn't. Plus if the fuel evaporates it leave residue behind that aren't in avgas.

These engines were designed in a time where lead was in all fuel. The lead lubricated the valves. That is why you hear of people sticking valves when using unleaded auto fuel. You need to use a lubricant if you use unleaded. I use MMO in everything I own and I put it in the oil and fuel. I was told by a guy that rebuilds cylinders to use a shot glass full for every 5 gallons. He has run it for 30 + years and never had a problem with it.

One of the biggest advantages of using auto fuel is that you can get the fuel with an octane level closer to what these engines were designed to run on. Most of the older engines were designed to run on 80 octane. When you use a higher octane, you will not get the performance that the engine is capable of. A lot of people don't realize that the higher octane fuels are needed in high compression engines because the fuel is actually harder to ignite. Premium doesn't do anything for a low compression engine except waste money and give you less performance. Do a search for "high octane in low compression cars" and you'll see hundreds of articles explaining it. That's why some people say that their plane runs better on Mogas. Because it does!

Has anyone seen any documented proof that auto fuel hurts engines? How about a accident report stating that auto fuel was the cause of the accident. I doubt you will. Most peoples opinions are formed on what they have heard and not what is actually proven. Call Petersons and ask how many engine failures happened due to auto fuel during their years and thousands of hours of testing to develop their STC. There is also the fact that over the life of your engine, you will have saved enough money to probably buy a new engine. I see no reason not to use it. As long as your flying regularly I think it's a great thing. Just hope we can get a dedicated source for E0 long term.
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Re: Autofuel VS avgas

Good point Jerry. Mogas does not store well. I fly enough it is not an issue for me. If I was only flying a hour a month I would have 100LL in it.

Also on my STC it requires you run something like a tank of 100LL every so often for lead for the valves. I can't remember the number. I travel enough I am way over the requirement. I burn mogas at home and 100LL while traveling. probably like a 50/50 split.

Good day
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Re: Autofuel VS avgas

Jaerl wrote:.... Just hope we can get a dedicated source for E0 long term.


Seems like there is a bit of a trend nowadays for stations to re-offer E-zero gas, and to put signage up advertising same. Apparently there are enough people with airplanes, motorcycles, old cars, boats, etc that want E-zero that the signs bring them in. I've heard of several 76 stations in western WA doing this- unfortunately none of the ones hear me are included. There is a newly reopened independant station about 10 miles from home offering E-zero premium, unfortunately it's not on the way to the airport but if my close-to-the-airport source dries up I'll be making the drive.
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