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**astjp2** · 08-11-2008, 17:47

Re: Avgas vs Autogas

The most common problem I have seen is lead fouling of the plugs, it can happen in as little as 50 hours. Go to your nearest bulk plant and see if they have mogas without Alkyhol in it (pun inteneded) you might even save money from not gettin it from the local gas station. Tim

Just test the gas when you buy it to make absolutely sure there is no Alcohol, and I like to blend 20% avgas with my mogas.

**crispy critter** · 08-12-2008, 06:02

Re: Avgas vs Autogas

Originally posted by gnflyn View Post

This subject may have been allready discussed, but I would like to hear some thoughts as to the following. In years past I used auto gas all the time and no problems, of course now all the gas I see in stations has ethenol added. The past year or so I have used 100ll exclusively with no issues so far. The question is, what are ramifications of using 100ll all the time? I am thinking lead buildup on valves, and what if I decided to try auto gas and got ethanol into fuel system. Is there any way to get no ethanol fuel from a gas station? Any idea on how many hours it might take for 100ll lead issues?

Over time the 100LL will also start to build up on the valves and valve seats. The guys in the higher elevations don't have this problem as much as we do in east ky or lower elevations.100LL also burns hotter and brings the CHT up and taylorcrafts are already known for poor cylinder cooling unless your running an open cowl. Ethenol is added at the bulk plant as they load the gas on the truck for delivery. Our local bulk plant said they would always have gas without ethenol availible. Not a lot of money difference but usually a cent or two on the gallon.
If you run gas laced with ethenol it might cause problems after a while. You will probably not see an instant problem but you might notice a slight power difference depending on how much of mixture is being used. You would probably never notice a 5% mix but over time it could start to cause problems with the seals in your carb,breakdown of your old fuel line,and corrsion in your fuel tank or any aluminium fuel lines(alcohol is corrossive to some metals such as aluminium). Now a 10% or 15% mix will probably cause less preformance on climbout,valve noise,hard starts,and might even cause vapor lock or pre-detination. My advice is run the 100LL or find a station or bulk plant who will sell you straight gas with no ethenol.

**Jim Herpst** · 08-14-2008, 10:57

Re: Avgas vs Autogas

hmm I keep hearing the evils of the alc in the mo gas . The biggest argument that makes sence is that the stuff holds water in suspence...which I not sure is all bad UNLESS it causes to ice up faster Hmmm Now in so far as it hurting parts .don't cars have tons of aluminum in their fuel systems?. Also I would like to know who has scientifically tested it with a a small continental motor to see what actually does happen?Kev have you read a publication on this and if so where? I want to learn more Not trying to be obstinate just trying to get out and at the facts . ( I have a habit of turning stones where snakes may lurk!!) I sure the stuff must be bad BUT I want to know who is actually testing.....

**M Jones** · 08-14-2008, 11:42

Re: Avgas vs Autogas

Just a throw in here, I've been trying to make up my own mind on the subject for a while now... I sat in on Don Sword's (Don's Dream Machines) forum at Airventure this year. Two things that in his opinion should not be used in aviation engines are Marvel Mystery Oil (in the oil), or auto gas. Don didn't comment on MMO use in fuel, but said any engine that they tear apart that's had MMO used as an oil additive will have all kinds of "junk" on the crank. Not to quote him, but apparently the "only" thing to be concerned with in the lower end are the center bearings, and Avblend seems to help there. (1 quart at the first use, 1/2 quart every oil change thereafter).

The burn rate differences between av gas and mo gas causes detonation problems he believes. This is just another opinion, but kind of hard to discount. I have friends that burn nothing but mo gas in their small Continentals, and have fewer problems that I've had with 100LL use, so I'm still not sure...

**Arnold Wallace** · 08-14-2008, 11:52

Re: Avgas vs Autogas

Jim,
It may be true that autos have aluminum parts in the fuel system, but could it be that those parts have a slightly different alloy which resists the corrosion formed with water/alcohol dissolved in the gasoline? I have found leaving mogas set in lawnmowers, chainsaws and other machines with cheap aluminum carburetors results in corrosion. LL100 does not make my 4 wheeler or 3 wheeler ATV run any better, but the gas keeps corrosion out of the fuel systems. Only another humble opinion - not the gospel truth!!!
N96175

**crispy critter** · 08-14-2008, 12:16

Re: Avgas vs Autogas

Originally posted by crispy critter View Post

Over time the 100LL will also start to build up on the valves and valve seats. The guys in the higher elevations don't have this problem as much as we do in east ky or lower elevations.100LL also burns hotter and brings the CHT up and taylorcrafts are already known for poor cylinder cooling unless your running an open cowl. Ethenol is added at the bulk plant as they load the gas on the truck for delivery. Our local bulk plant said they would always have gas without ethenol availible. Not a lot of money difference but usually a cent or two on the gallon.
If you run gas laced with ethenol it might cause problems after a while. You will probably not see an instant problem but you might notice a slight power difference depending on how much of mixture is being used. You would probably never notice a 5% mix but over time it could start to cause problems with the seals in your carb,breakdown of your old fuel line,and corrsion in your fuel tank or any aluminium fuel lines(alcohol is corrossive to some metals such as aluminium). Now a 10% or 15% mix will probably cause less preformance on climbout,valve noise,hard starts,and might even cause vapor lock or pre-detination. My advice is run the 100LL or find a station or bulk plant who will sell you straight gas with no ethenol.

Jim,
I got most of this info from talking to people at the bulk plants for both auto and av gas. As for the build up on the valves and stuff...that's mostly from personal experince.

**crispy critter** · 08-14-2008, 12:29

Re: Avgas vs Autogas

Originally posted by M Jones View Post

Just a throw in here, I've been trying to make up my own mind on the subject for a while now... I sat in on Don Sword's (Don's Dream Machines) forum at Airventure this year. Two things that in his opinion should not be used in aviation engines are Marvel Mystery Oil (in the oil), or auto gas. Don didn't comment on MMO use in fuel, but said any engine that they tear apart that's had MMO used as an oil additive will have all kinds of "junk" on the crank. Not to quote him, but apparently the "only" thing to be concerned with in the lower end are the center bearings, and Avblend seems to help there. (1 quart at the first use, 1/2 quart every oil change thereafter).

The burn rate differences between av gas and mo gas causes detonation problems he believes. This is just another opinion, but kind of hard to discount. I have friends that burn nothing but mo gas in their small Continentals, and have fewer problems that I've had with 100LL use, so I'm still not sure...

I don't like using MMO in the oil either but I do like it occasionally in the gas because it helps break down lead and carbon build up on the valves and also helps clean the carb.

As for auto gas.....we have a C-170 that runs twice more 100LL then auto fuel and in 500 hours it has had several cylinders pulled because of cracked heads,burnt exhaust valves,and carbon build up. The 1959 C-172 setting in the hanger next to the C-170 runs 98% of the time on nothing but straight regular unleaded auto fuel,the only time it has 100LL is when it goes on a long cross country where mogas is not availible and most of the time my uncle plans his cross country fuel stops at places that do have mogas,either way he rarely ever flies cross country and his airplane has a little over 600smoh and has never had a cylinder problem or any other problem. The low compression engines run better and longer on low octane.....with that said,if you only fly once every other month or so then I highly recommend 100LL because the auto gas will gos bad over time and cause all kinds of fuel problems.

**flybikefarm** · 08-14-2008, 14:30

Re: Avgas vs Autogas

I have over 400 hours on the 65 in my cub since rebuild. I run mostly mid grade BP auto gas, keep about two or three month supply on hand. I also ran mostly auto fuel in the C150 I used to own, no cylinder problems in 600 plus hours. Just my own observations. George

**NY86** · 08-14-2008, 14:34

Re: Avgas vs Autogas

I've never seen any concrete evidence that mogas causes any problems in these engines. Problem is any engine with problems, if it ever used mogas, that's where the blame ends up. Like the avgas engines never have any issues...

As far as any gas with ethanol in it goes, I don't like it. It's OK, I guess, for newer cars, mainly because it doesn't stay in there long. However, ethanol attacks some older rubber compounds and the shellac used on floats. Mogas with ethanol is less stable and attracts water, neither of which lend it to use in aircraft. I don't even like using it in my lawn mower, but I don't have a lot of choice there.

MMO is mostly mineral spirits. Why would anyone want to pour mineral spirits into their oil sump?

**M Towsley** · 08-14-2008, 17:04

Re: Avgas vs Autogas

Kevin,

The average longevity is 6 months for autogas, 12 months for avgas.

**Jim Doody** · 08-15-2008, 05:57

Re: Avgas vs Autogas

In regard to the the use of Avblend, I believe they recommend 12 oz. in a 4-8 qt oil system. Are you sure of Don Swords recommendation? Thanks Jim

**M Jones** · 08-15-2008, 08:03

Re: Avgas vs Autogas

Originally posted by Jim Doody View Post

In regard to the the use of Avblend, I believe they recommend 12 oz. in a 4-8 qt oil system. Are you sure of Don Swords recommendation? Thanks Jim

Thats what I heard and made a note of, but if I were going to use it myself, the Avblend recommendation makes sense. Thanks.

**Guest** · 08-16-2008, 21:06

Re: Avgas vs Autogas

Our little A-65 will run on 73 octane, that's the reqiurement in the type certificate last I looked.

Hard to imagine that a bit of ethanol will drag 87 octane done to less than 73.

Mine has run great on mogas for 15 years or more, BUT gas with ethanol is excluded from my stc and I don't use it.

I think it has more to do with alcohol being a solvent for the sloshing compunds than anything else.

Dave

**Ragwing nut** · 08-16-2008, 23:38

Re: Avgas vs Autogas

The high lead content of 100LL will cause carbon build up on the valves and over time short of long will cause a stuck valve. I have seen it many times over the years of rebuilding engines and maintaining small aircraft. Very common problem. I always told my customers to run a blend.

If you use the ni-resistant guides and valves, the guides will wear and prevent stuck valves. The draw back is that they won't go to TBO.

It is illegal to use any mogas with alcohol per the Peterson STC. Not only will it corrode aluminum, it also lowers the boiling point of mogas making it more suseptable to vapor lock.

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