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93 octane w/o ethanol

721lp
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721lp Collaborator

721lp

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Anyone considered using 93 octane auto fuel (without ethanol obviously)in their O360? A friend of mine is doing just that. Uses one tank of 100LL and one of 93 and alternates them. Uses the 100LL for t/o and landing. Just curious as to the wisdom of this. He's been doing this for a while now with no obvious ill effects. Been thru 3 annuals with no problems. Let's hear it guys.......


 

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kortopates Grand Master

kortopates

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I assume he’s well aware its not approved/legal for Mooney’s


Per the Mooney TCDS:


IV. Model M20C, 4 PCLM (Normal Category); Approved October 20, 1961


Fuel 100LL or 100/130 min. grade aviation gasoline (See Note 9)


NOTE 9: 91/96 Min. grade aviation gasoline acceptable for Model M20C aircraft, Serial Nos. 1940 through 3184


If you search around on the internet, you’ll see part of the rumored explanation for why the Mooney doesn’t have an STC for mogas is concerns of vapor lock. But I have no credible references to point to. In the same concern Scott voices, one thing such use can result in, is an immediate lawsuit  as soon as anything went wrong with passengers involved; at least here in CA its virtually guaranteed.

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sleepingsquirrel Mentor

sleepingsquirrel

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The Lycoming O360 A is ok by Lycoming for 93 octane automotiive fuel with ethanol of less than 1%. They go on to say that that an STC is required for the airframe the engine is in.  I just looked it up today and have the reference at my work computer. Eventually all of us will be looking for an alternate fuel for these old engines. The summer fuel is better for vapor pressure (aviation ) than the winter mix.

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721lp Collaborator

721lp

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I guess what I really am interested in is how the same engine can be approved in one airframe for auto fuel and not another. Does the engine know what airframe it's in? I guess it all comes down to legalities, like everything else.......

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KSMooniac Grand Master

KSMooniac

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Yes, it is entirely dependent on the airframe installation, and the rest of the fuel system.  In our case, a low wing with a different fuel system and fuel pump than say an old Cessna with a high wing and gravity-feed system.  The vapor lock issues could not be reliably solved in the Mooney installation, so no STC was issued.  There could also be issues with the sealant in the Mooney tanks vs. the separate tanks used in other airplanes, but I don't believe that is a big concern with ethanol-free mogas.  (Ethanol does a lot of damage to all kinds of fuel system components in airplanes and boats)

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sleepingsquirrel Mentor

sleepingsquirrel

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I think that if you have a highwing plane with head pressure on the fuel lines vapor lock is less likely. If you have fuel pumps internal to the tanks vapor lock is less likely. If the fuel pump has to lift the fuel from the tanks, vapor lock is more likely to happen. The lower the ambient pressure and the higher the temperature the more likely it is to have vapor lock. The same engine in different airframes can possibly make a difference. I think the evidence is one can burn auto fuel but without a blessing from extensive testing you are on your on. Subject to violations , and possibly fuel starvation in some cases. People have been doing it for years. I have not read accident reports identifying auto fuel as the cause , just lack of fuel or water in the fuel. Has anyone else read of auto fuel identified as the cause of engine stoppage? ( discount ethanol contamination)   

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sleepingsquirrel Mentor

sleepingsquirrel

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I think the reasoning is that lead additive is more than necessary in 100LL but non- existant in no lead. So instead of mixing no lead and low lead to get the proper lead additive level it's just easier to run a tank of low lead periodically to boost the lead in the subsequent no lead fills. This probably works for the low compression engines just fine but for higher compression engines one would want to mix fuels to get the lead additive consistant and proper.


I think the reasoning for left tank of auto fuel and right tank of 100LL av gas is to cover take off and landing, take off and land on the good stuff , switch to the auto for cruise.


Just thinking outside the box, but why couldn't the vent system on the Mooney be directed into the airstream like the Cessna with a 90 degree elbow? The impact air would allow slight static pressure on the fuel in the tank  to help prevent vapor lock on a tank with auto fuel. I don't know if this was tried in and attempt to obtain an STC for the Mooney , I'm not sure if anyone has even investigated an STC for Mooney.


 

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Shadrach Grand Master

Shadrach

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Quote: sleepingsquirrel

I think the reasoning is that lead additive is more than necessary in 100LL but non- existant in no lead. So instead of mixing no lead and low lead to get the proper lead additive level it's just easier to run a tank of low lead periodically to boost the lead in the subsequent no lead fills. This probably works for the low compression engines just fine but for higher compression engines one would want to mix fuels to get the lead additive consistant and proper.

I think the reasoning for left tank of auto fuel and right tank of 100LL av gas is to cover take off and landing, take off and land on the good stuff , switch to the auto for cruise.

Just thinking outside the box, but why couldn't the vent system on the Mooney be directed into the airstream like the Cessna with a 90 degree elbow? The impact air would allow slight static pressure on the fuel in the tank  to help prevent vapor lock on a tank with auto fuel. I don't know if this was tried in and attempt to obtain an STC for the Mooney , I'm not sure if anyone has even investigated an STC for Mooney.

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DaV8or Grand Master

DaV8or

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My question for Mogas users is, how do you know for sure there isn't any ethanol in the fuel? Here in California, it's a moot point. I have no idea where you would buy ethanol free gas.

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N601RX Grand Master

N601RX

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If you go back and read the original post, he said his friend was using 100LL for takoff and landing and only using the Mogas for cruise at altitude.  He is doing this to Min the risk of vaporlock.  At crusise power settings at say 7500 the under cowl temps are going to be much lower  than at takeoff and climb.  The air temps are going to be much lower up there also, so that is why he is not haing any trouble with vaporlock. 


Still doesn't make it legal, but I've heard of others at our airport doing the same thing.


 

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