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Thread: reg unleaded fuel?

  1. #1
    Member tboehm's Avatar
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    Default reg unleaded fuel?

    I have noticed a couple of posts where some members stated something about planes that were capable of burnning reg unleaded. What kind of planes are capable of doing that? Any additional pluses besides cost? What if any, are the limitations of using it? What does it do to preformance? Sorry for the rookie q's but would appreciate some insight.

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    Moderator Adison's Avatar
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    Default Fuel

    Its been awhile since I looked at this but if I remember correctly it is just an STC from the EAA. I think it only applies to the Lycoming O-320 series of engines but I could be wrong, like I said its been a few years.
    Basically it a piece of paper and some decals that you apply and a data tag for the engine and you can then burn 97 octane unleaded auto fuel in your aircraft instead of the 100 octane lowlead avgas. The lower octane I believe will decrease your horsepower some but you save money by being able to buy lower cost fuel and find fuel anywhere you go. There is also the issue of using unleaded fuel and the extra wear on your valves due to the lower lead content. Like I said, its been a few years since I looked at this and I could be way out in left field by now. Talk to one of the engine overhaul shops in twon and ask their opinion on the subject.
    Adison
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    Member Float Pilot's Avatar
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    The older original leaded aviation fuel was 80/87 octane for most general aviation aircraft. So some of the older engines do not realy like 100LL all that much.. My old 0-290D2 135 hp and my C-90 run hotter and burn more fuel if I use straight av-gas. The older 0-470s in C-180s do just fine on auto gas as well.

    The STC's to burn auto-gas can be issued for several engines with lower compressions.
    One of my students has one for his 0-300 (C-145) powered Cessna 172.
    My C-90 powered PA-11 has one as well. Although my engine likes a mix of av-gas and unleaded, with a shot glass of MMO.

    Just make sure you avoid gas with alcohol in it. The alcohol and water will mix with each other, plus alcohol does weird things to certain types of gaskets and seals. Not to mention the older style carb floats... When you get the STC they have a little test tube to check your fuel for alcohol... Basically you have water in the bottom of the tester, then you add your gas. If the water level raises thenthe alcohol was attracted into the water and increased the volume...
    Floatplane,Tailwheel and Firearms Instructor- Dragonfly Aero
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  4. #4
    Member tboehm's Avatar
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    Default how old?

    Quote Originally Posted by Float Pilot View Post
    The older original leaded aviation fuel was 80/87 octane for most general aviation aircraft. So some of the older engines do not realy like 100LL all that much.. My old 0-290D2 135 hp and my C-90 run hotter and burn more fuel if I use straight av-gas. The older 0-470s in C-180s do just fine on auto gas as well.

    The STC's to burn auto-gas can be issued for several engines with lower compressions.
    One of my students has one for his 0-300 (C-145) powered Cessna 172.
    My C-90 powered PA-11 has one as well. Although my engine likes a mix of av-gas and unleaded, with a shot glass of MMO.

    Just make sure you avoid gas with alcohol in it. The alcohol and water will mix with each other, plus alcohol does weird things to certain types of gaskets and seals. Not to mention the older style carb floats... When you get the STC they have a little test tube to check your fuel for alcohol... Basically you have water in the bottom of the tester, then you add your gas. If the water level raises thenthe alcohol was attracted into the water and increased the volume...
    When you are talking about older, how old are you talking about. I've been toying with the idea of something like a c-180 but having a tough time deciding what to get. I want something that I can do floats, skis, and off strip work and carry 3 with gear. But the thought of getting something that would work on reg unleaded seems like a good idea.

  5. #5

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    I have an auto fuel stc for my cessna 150/ o_200 Continental. Have just replaced 2 cylinders and cleaned the valve quides in the other 2 I am sceptical of any benefits in the long term. If I have to use auto fuel I will mix it with 100LL and test for ethenol before use. 100LL has about 4 times
    as much lead as the old 80 oct. that older engines were designed for so that presents problems as well.

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    The only problem I have had with unleaded fuel is it seems to build carb ice much faster than 100 LL. I think most aircraft engines also need some lead. I have found if you try to save money on fuel you end up spending it on repairs later. If the lead causes valve problems just put a little Marvel Mystery oil in and it will cure that problem.

  7. #7

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    Cub Driver, how much MMO per 10 gals of 100LL?? I have started using a quart with the crankcase oil and adding some to the gas but always willing to listen and learn from others.

    Thanks

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    A quart of unproven/unapproved oil in your crankcase? For what?

    MMO instructions call for 4 oz per 10 gallons of fuel as a "top oil". I've never seen any evidence that it's beneficial. I know that when there's MMO in the gas and you sump a few drops of water from your tanks? The water is red. I never understood how water soluble dye and perfume were supposed to be good for my engine.

  9. #9

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    Having been used in aircraft engines since WW2 I would think if any harm came from MMO we would know by now. One hour in the crankcase cleaned "stuff" out that I would rather not have in the oil. When the breakin is complete I will run Aeroshell 80. I have added a spin on filter so I can do an easy oil change and see whats trapped in the filter.

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    You've used it in aircraft oil since WWII? If not you, who? Does TCM or Lycoming recommend it, or better yet, even allow it? Any big engine rebuild shops like RAM or Lycon? ECI? Superior? Who then? How about the FAA?

    What's your oil's viscosity index after you cut it with 15-20% MMO? If a little is good, why not use more? Who decided what concentration was best? Does it matter what kind of oil you're adding it to? Should a guy use more with 50 weight than with 15-50? What about 20-50? Where can I get information that answers these questions?

    The topic started as a discussion about mogas. Since you don't worry about adding gobbelty-goop to your oil, why worry about fuel standards? Obviously car gas burns?

  11. #11

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    We are stuck with many things in GA because of FAA mandates and regs that are unfounded except in a court room. I am not one to stray too far outside the box when in the airplane but I will have a look. Do you not agree with MMO added to gas that has too much lead for an old engine?
    TCP was used but is bad to carry in the plane and bad for the envirnment when used. Just one more problem caused by well thinking people in our government.

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    I'll freely admit that I used MMO in my fuel for several years. After a conversation with a petrochemical engineer who's also a pilot I stopped using it a couple of years ago. I've seen absolutely no change. That makes me wonder why I ever used it in the first place. I can honestly say I've never had a lead-related problem of any kind and I've always used 100LL. Lead-related problems might be solved using a lead scavenger like TCP in the fuel, and MMO may have some similar solvent properties, but I can't imagine why anyone would compromise with their engine oil by adding it.

  13. #13

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    MMO was introduced in the crankcase to help clean up an old engine. We added it to the gas for obvious reasons. I plan to discontinue using it in the oil after breakin/first change. BTW MMO had a MIL-SPEC number when it was used by the military. Of course so did 30M1 Ball ammo but then I know which of them was more effective for intended purpose. Have a great day. This has been fun!

  14. #14
    Member Float Pilot's Avatar
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    I still remember the old FAA DC3 sitting here with a huge can of MMO in the cargo bay.

    I used an av-gas / mo-gas blend in a 0-320, with a shot glass of MMO on every gas fill up and that engine had 3,600 hours on it when I sold the plane to a guy in Nevada who is still flying it. I also put some in the crank anf ran it fountil hot just before every oil change. (I change oil every 25 tach hours) I had changed the jugs twice.

    Before the change in fuel mix, that engine developed a lot of lead on the plugs. (instruction plane) I had to clean them every 20 hours.

    I have also used MMO to remove lead from rifle barrels so it does something...

    Maybe it's just plain magic...
    Floatplane,Tailwheel and Firearms Instructor- Dragonfly Aero
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    Have you tried Stoddard Solvent on your rifle barrels? According to the MMO MSDS that's what the mystery ingredient is. That and a tiny shot of carburetor cleaner.

  16. #16

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    I have not. Still use Hoppes for general cleaning and 7.62 for copper fowling.

  17. #17

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    Two supplemental type certificate authorizations are available for auto fuel use in certificated aircraft - here is the link to one - the Petersen STC: http://www.autofuelstc.com/ It lists the engines and aircraft that are eligible. You have to match both the aircraft and engine combination to qualify.

  18. #18

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    Quote Originally Posted by cubdriver55 View Post
    The only problem I have had with unleaded fuel is it seems to build carb ice much faster than 100 LL.
    I have noticed that too, as recently as Saturday. I'm not sure of the science behind it but it seems to be more than just coincidence. But that is what carb heat is for - what with the more-than-one-dollar spread between 87 UL and 100LL I'm likely to continue to fill my gas cans at the Tesoro station instead of at the airport ramp whenever I can.

    About every fourth or fifth fill up I use 100LL to keep some lubricating lead on the moving parts, but even with aggressive leaning I have to use TCP with every tank of 100LL - my engine just doesn't like the high lead content very much. It's just like a discussion about religion or politics but I see no downside to auto fuel as long as you can avoid the ethanol ridiculousness going on Outside.

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    Member algonquin's Avatar
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    I flew for a company in the early 80's that used auto fuel in the trainers (C-150) and the engine would quit if you pulled the throtle back too quick, then you had to pump the throtle to relight it. Also in the 172 the auto fuel would vapor lock above 7000' on warm days and come back to life when you decended. Please consider maintence at this company wasn't their strong suit. I still don't use auto fuel to this day.

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    There is a article in FAA aviation news that discusses it throughly.

    Some aircraft run much better on auto fuel. Problem is ETHANOL Which will cause vapor lock, it may deteroate your rubber seals and will desomate fiberglass tanks, ethanol will also accumulate 140% more water then your sediment tanks are required to handle. Hence the reason that using ethanol fuel is not covered by the STC.

    These guys have the STC for most aircraft you can use autogas in, they also have a DIY test procedure to see if your gas has ethanol in it

    http://www.autofuelstc.com

    Marine fuel tends to stray away from ethanol, so if your local gas stations have ethanol, your local dock might be your next try.

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