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Mogas or Avgas?

szq

Registered User
I have a Mogas STC and have ethanol-free 93-octane mogas available locally, but have heard from some people that mogas will gum things up and is just generally a bad idea... But I've also heard that the lead in Avgas can also cause cylinder problems. Other than fouled spark plugs I hadn't heard of lead being a concern for a Lycoming O290. Am now wondering if Avgas is part of the reason two cylinders had slightly low compressions recently (with leakage into the exhaust), as I've been using more Avgas than Mogas lately while the previous owner used mostly Mogas (low time engine overhauled ~ 5years ago). Is it the lead burning causing buildup on the valve face? Buildup on the valve stem guide, causing asymmetry in seating and then the valve face issue? Other than simply geometrical tolerances being too loose or poor baffling causing a cylinder to run too hot, what else could cause low compression to develop?
Starting to hear all sorts of 'old wives tales' about Avblend and Marvel Mystery oil and all sorts of other things 'fixing' low compressions, none of which I trust. Looking for any technical advice on these issues, and especially whether Avgas or Mogas is a better choice.
 
There are downsides to each type.

Mo-gas does not keep well when stored in aircraft tanks.

Use of CLEAN containers & proper safety precautions is a must with either type.

Anyone that is using 100LL should become familiar with Lycoming Service Lettter SL185B.

Sorry I don't know how to send a link.

Among other things it tells you how to shut down the engine.

It details RPM to 1800 ( remember this is Lycoming-not Piper) .

This scavenges lead from the Combustion Chamber.

It also is an excellent time for your Post-Flight Mag Check which will tell you whether you are ready for the NEXT flight .

My opinion is the worst engine with lead fouling is the O-235L2C.

However; using these procedures ELIMINATED the problems.
 
I have been running 100% mogas for over 50 hours now. I run 91 E0 in my O-360. Flown it in 95*F down to 10*F. No problems whatsoever. Plugs are clean, no fouling. I don't use MMO either. They only con is the smell and brown stain instead of blue. If I spill any I make sure to clean up quickly.

 
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Thanks for the SB reference -- I try to educate myself as much as possible and have read various guidelines from Lycoming, but had never heard this information before. Very good to know!
 
Here's the specific verbiage from the Lycoming Service Letter:

4. Prior to the engine shut-down, the engine speed should be maintained between 1000 and 1200 RPM until the operating temperatures have stabilized. At this time, the engine speed should be increased to approximately 1800 RPM for 15 to 20 seconds, then reduced to 1000 to 1200 RPM and shut down immediately using the mixture control.

 
Easier to repeat. On the small Continentals, I have found 75% regular, 25% 100LL is better than a steady diet of either.

I am actually afraid to do that in the Super Dec, because I am not sure about compatibility with rubber components in the fuel injection system. I do know that the older MTBE fuel ate stuff at an alarming rate. It would save me a lot of spark plug hassles, so as soon as I am sure about the MTBE and other chemicals, I will get the STC.

Picked up a 195 in the Midwest. Guy selling it is older than me, and builds up Jacobs all year long. Puts MMO in the gas religiously. I cannot tell the difference, but that was good enough for me. I really learned to respect the guy in very short order.
 
I've run straight mogas, straight 100LL and a blend of both for many years now and the only thing I've had trouble with is the cork gaskets, if you run 100% of eather and switch back and forth you will fine that the cork gaskets will start to leak, this is because mogas will swell the gasket and then 100LL will shrink it back and cause it to leak. mainly carb. bowl and sight gages.
 
Isn't the future Jet fuel anyway, last I heard there are some availability issues in some areas for avgas other than that it is more expensive.
 
Make sure you keep the gas fresh you shouldn't have any issues. If the gas has sat in the tanks more than a few weeks I tend to drain it and put it in my tractors or other equipment and put fresh fuel in the plane.
I have been running mo-gas in 3 different planes almost exclusively. One of them has been burning it for 25 years. I occasionally run or mix in some 100LL in each of them except for the RANS S-7 which has only had 91 octane mo-gas used since I have owned it. In all these years the only thing I have had to do is replace an O-ring in the primer but I can't say for certain that it was due to mo-gas use. I had the plane stored for several years while I was overseas and someone stole all the 100LL I had in the tanks so everything dried up. It was stored in AZ in an old WWII multi-bay hangar .
The
 
An old thread but I'll add my .02. I've been using 50/50 110LL/unleaded mogas in my 150hp O-320 PA-12 for years now and have no issues at all. The plugs love it: I never have to clean them between annuals. Runs strong and smooth with good power at elevation on glaciers. Only irritating thing is the brown residue I get in the sight gauges after a couple of years.
 
Got to reerect this thread with the simple question............. I realize lots of folks use high test car gas that is ethanol free by itself and lots of different blends mixed with 100LL, but I just had an old friend from Dillingham , tell me he and a bunch of the cub guys out their are running
Reg car gas WITH ethanol in their engines??? Can some of the guys that are running it please comment on how this is working out?
 
Got to reerect this thread with the simple question............. I realize lots of folks use high test car gas that is ethanol free by itself and lots of different blends mixed with 100LL, but I just had an old friend from Dillingham , tell me he and a bunch of the cub guys out their are running
Reg car gas WITH ethanol in their engines??? Can some of the guys that know anything about ethonal, please comment on how this would probably work out?
 
I would never admit to doing something so illegal, but I note that my ancient Mustangs run just fine on the stuff, and my daily flyer Cub would probably not have a bit of trouble with a 25/75 mix if I were to run it that way for the last three decades. No way, I never do anything that is outside the regs.

Been a long time since this thread started, but in the same vein, for those of you who use this Lycoming full power shutdown technique, it is best done aimed at somebody else's hangar.
 
LOL, Bob, well I certainly wouldnt expect anyone to admit anything about it, but am curious about say "experimental or non cerified aircraft" that are using it [if that makes it easyer to discuss it] and I am going to assume the 25/75 blending is 25 car gas, and 75 of the blue stuff???? Or the other way around???? Interesting subject for sure, with car gas getting into the $$$$ two dollar range....................... of course we ran thousands of gals of car gas over the years [non ethonal] and always used to dump one quart of MMO into a 55 gal drum of gas, never had ANY problems with that brew in O320s in Cubs.................... ran just fine , like to hear more on this .
 
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I have been running 98 for the last year in the Cub ( o-375) and RV6 (o-360) and I use the red knob.

Questions from me are:

Why do I get better fuel economy in the RV from 98 compared to Avgas? At altitude and lean of peak I get 2 L/hour better. Does not make sense but have proven it time and time again. Some one said that the engine is probably running smoother (less bang) therefore I am leaning more aggressively.

Would 98 store better than 95 or 93??

Colin
 
Got to reerect this thread with the simple question............. I realize lots of folks use high test car gas that is ethanol free by itself and lots of different blends mixed with 100LL, but I just had an old friend from Dillingham , tell me he and a bunch of the cub guys out their are running
Reg car gas WITH ethanol in their engines??? Can some of the guys that are running it please comment on how this is working out?

I've used more then a thousand gals before efree became available again. When on floats you burn what ever you can find. If you put Startron in it you won't have any swollen gaskets and it won't absorb water anymore. 89 runs great at 8.6:1

Glenn
 
Thanks Glen that is plenty to have had a problem, if there where any, looks like it certainly has potential, like to hear more and any weird problems others may have heard about? I haved used alot of these stabilizers in ethanol gas for my outboards and skidoo, but thought its only merit was to prevent
Phaze Seperation, so didnt know anything about it preventing swolen gaskits, which is of course ,exactly
The problem that is of concern?
 
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I understand many other Rotax users are hesitant to use E-10 gas, and like myself, though they use pure mo-gas at home, (if they are lucky enough to have a source), on a XC they will resort to using (gasp) Av gas. Not me, I have used lots of E-10 in the last couple years when unable to get pure, and I simply can't tell ANY difference. Not real sure how that relates to you burning it in a Lyc., but for me anyway it's a total non-issue. I do draw the line at filling my home bulk tank with it and letting it sit there for a while, for that I use 100% good old gasoline. All of the E-10 I have bought was burned within a week or so, FWTW.
 
We've run mogas in our PA-12 and C-180 for years and have never had an issue with it not staying good as long or gumming anything up. I've read articles that say if you run mogas - the money you'll save will pay for your major overhaul, and that 100LL has way more lead than is needed. We always ran a tank or 2 of avgas as you do need some lead for lubrication so we always did a minimum of a tank per season which is easy enough as not all airports have mogas.
I'd personally have no hesitation about running mogas for all operations, but also not hesitant of putting in 100LL when it's all that's around.

Just my opinion.
 
Richard,
I am guessing when you say Mogas, you are likely referring to NON ETHONAL fuel are you not????????? The question here is Who has experience with This 10% Ethonal stuff we are all stuck with weather we like it or not.
I also have burned many thousands of gals of Mogas but It did NOT have any ethanol in it ??? I know you guys out in Mn have the non ethanol stuff available much more readily; than it is back here on the East Coast, I had a friend from Ely tell me he was paying $3.50 gal for 91 Oct mogas[non ethonal] out there last fall......................... however at the same time, here in Maine, they were charging us, $5 bucks for it! At the darn few places you can even get it.............. I questioned this from one of the places that has it , and he claimed the reason it was so expensive here is that it had to be brought into Maine from Quebec??????? Funny thing is my buddy that drives a tanker, for a local gas distributer here, told me that the fuel at the depot, they buy it from, is all reg fuel[non ethanol] and he has to set the computer to have it" ADD the 10%" when he fills the tanker................ anyway I am guessing our representiive Angus King, will do everything they can to make it almost impossible to get it here...............
 
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No - read between the lines. If the stuff works in my ancient Mustangs - they each make a round trip to the airport once a month - then it probably works in an even more ancient Continental or Lycoming. 100LL has four times the lead of old 80 octane, and the little Cubs had a minimumof 73 octane.

I would be hesitant to use alcohol if I only flew my airplane once every other month, but flying it every day would probably make phase separation the same kind of problem that it is in your Mercedes.

As for legality, I would never admit to using MMO either - it is just as illegal as mogas with alcohol - but a lot of very savvy restorers use it, and it does not seem to hurt anything.
 
Richard,
I am guessing when you say Mogas, you are likely referring to NON ETHONAL fuel are you not????????? The question here is Who has experience with This 10% Ethonal stuff we are all stuck with weather we like it or not.
I also have burned many thousands of gals of Mogas but It did NOT have any ethanol in it ??? I know you guys out in Mn have the non ethanol stuff available much more readily; than it is back here on the East Coast, I had a friend from Ely tell me he was paying $3.50 gal for 91 Oct mogas[non ethonal] out there last fall......................... however at the same time, here in Maine, they were charging us, $5 bucks for it! At the darn few places you can even get it.............. I questioned this from one of the places that has it , and he claimed the reason it was so expensive here is that it had to be brought into Maine from Quebec??????? Funny thing is my buddy that drives a tanker, for a local gas distributer here, told me that the fuel at the depot, they buy it from, is all reg fuel[non ethanol] and he has to set the computer to have it" ADD the 10%" when he fills the tanker................ anyway I am guessing our representiive Angus King, will do everything they can to make it almost impossible to get it here...............


I use what we call MOGAS 95 (5% ethanol) in Europe since more than 10 years in my SC (O-320 A1A) and WACO (W-670) without any problems. Maximum altitude for my operation is 5000ft MSL, moderate climate.
Even for bannertowing in summer with my SC , no problems.
BUT one year ago, I exchanged all flexible fuel hoses. The old ones were very old and stiff. I used Aerouip 303. After two days, the fuel in the gauges turned brownish!
I had put a short part of hose in a glas of MOGAS, when I started the job. So I went and checked my piece of Aerouip 303. It was swollen and soft! After a week, it looked almost like a black marshmallow.
So I changed all hoses again, using a french brand for automobils and aviation (not certified). Living in the US, I'd gone to NAPA.

Thore
 
The problem is Frenchy, that in the near future we may not have a choice anymore. Ethanol free gas is already becoming harder to find.
 
In Alabama, (high humidity) small engines(lawn mowers) get destroyed pretty quick by e-autogas; in Utah, (low humidity) no apparent problem....the e-autogas gets slightly acidic when it absorbs water, and becomes cloudy. Have not seen that around here.
 
takes twice the amount of ethanol to make the same energy
Maybe should read up on that statement since that's not right.
corrosion will eat your aluminium tanks slowly
I know of a big Continental that has aluminum fuel lines feeding it for over 8 years and they don't leak yet. This person seals up the vent between flights and trys to add fresh fuel just before flying. Also, has a teflon fuel line to the carburetor.
 
IMHO the 666 Teflon hose is the only safe hose to use. First thing I do to something new is change gascolator hose to 666.

Glenn
 
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