This is probably a dumb question but....

[bcg]

I'm reading the POH for the M20C and it says that the engine uses 91/98 octane fuel.  Obviously the 110 octane AVgas is good but, what about 93 octane Mogas?  It's above the 91 octane minimum...

 

I don't mind buying Avgas, it's really more convenient than hauling in cans of Mogas, but in a pinch it would be nice to have the option.

[N201MKTurbo]

The octane numbers for aviation fuel is calculated differently than the octane numbers for auto fuel. They are not the same.. 

[carusoam]

Post a pic of the POH page…

The challenge with using auto fuels….  Is their ability to get absorbed into seals and other plastic and rubber items… they can swell, and stop sealing…

The fuel approval process for our planes means that all of the additives and chemical formulation have been tested…

From tank to tail pipe…

 

trying to be a fuel chemist when 100LL is not available… is going to be extra challenging…

PP thoughts only, not a chemist.

Best regards,

-a-

[M20F]

Premium car gas would work in a O-360 without causing detention.  
 
It is illegal as there is no STC that is due to vapor lock issues when testing for said STC, so probably not a wise idea from a safety perspective either.  In general low wings have vapor issues and thus why the STC is only around for high wings in general. 

Ethanol mixed gas isn’t good for various parts and for the most part today it is hard or expensive to avoid it. 

[MikeOH]

40 minutes ago, M20F said:

Premium car gas would work in a O-360 without causing detention.

Wow, wish I'd known that in high school; if I'd just sprung for premium over regular....

[bcg]

3 hours ago, carusoam said:

Post a pic of the POH page…

The challenge with using auto fuels….  Is their ability to get absorbed into seals and other plastic and rubber items… they can swell, and stop sealing…

The fuel approval process for our planes means that all of the additives and chemical formulation have been tested…

From tank to tail pipe…

 

trying to be a fuel chemist when 100LL is not available… is going to be extra challenging…

PP thoughts only, not a chemist.

Best regards,

-a-

Here you go.

[bcg]

1 hour ago, M20F said:

Premium car gas would work in a O-360 without causing detention.  
 
It is illegal as there is no STC that is due to vapor lock issues when testing for said STC, so probably not a wise idea from a safety perspective either.  In general low wings have vapor issues and thus why the STC is only around for high wings in general. 

Ethanol mixed gas isn’t good for various parts and for the most part today it is hard or expensive to avoid it. 

Good point.  I have easy access to ethanol free fuel but, it's only 89 octane and it costs about the same as Avgas.

[Guest]

From the type certificate.

 

[Joshua Blackh4t]

Lycoming published something about it. They approved standard grade fuel but with the caveat of various quality controls. Then pointed out that the quality controls can't be done with standard fuel so we're stuck with avgas.

If someone made a low octane avgas, it could be used, but it doesn't exist.

[carusoam]

This is where the wheels fall off…

1) The older POHs for the M20C we’re saving money by printing the least amount of words…

2) the most recent POH for the M20C expands on the details quite a bit….

3) DOC pointed out where it has two parts to the description… Octane, and aviation gasoline….

4) A copy of the most recent M20C POH follows… where the two parts make it to the POH…

5) Recommendation…

• get the most recent POH for the plane to supplement what you have….
• And a copy of the Type certificate is really helpful too….
• while gathering documents… the engine manufacturer wrote an ops manual for the engine itself….

PP thoughts only….

-a-

 

 

[bcg]

Thanks all, I learned something today so it's a good day.

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[kortopates]

Lycoming published something about it. They approved standard grade fuel but with the caveat of various quality controls. Then pointed out that the quality controls can't be done with standard fuel so we're stuck with avgas.
If someone made a low octane avgas, it could be used, but it doesn't exist.

Swift UL94 has limited availability.


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[cliffy]

OK School time:-)

What color was 91/96 octane fuel when it was available?

Bonus question

What was different about the engines approved for 91/96 as opposed to those with the 100/130 restriction?

 

[Fly Boomer]

1 hour ago, cliffy said:

What color was 91/96 octane fuel when it was available?

Seems like it was green.  The 80 octane stuff was red I think.

[PT20J]

20 minutes ago, Fly Boomer said:

Seems like it was green.  The 80 octane stuff was red I think.

Green was 100/130. That was the stuff we used before 100LL (blue). The placard on my fuel caps reads: FUEL - 100 (GREEN) or 100LL (BLUE) MIN. OCT.

Skip

 

 

[cliffy]

YUp keep trying for the 91/96 

[EricJ]

18 minutes ago, cliffy said:

YUp keep trying for the 91/96 

Wiki sez brown, which I don't think I've ever seen.    When I was a lineboy at a military flying club we bought 115/145 from the Army and that stuff was a beautiful purple color.   I miss that stuff as it was gorgeous.   Always liked looking at it from a sump or something.

  

[cliffy]

Using Wiki was cheating

Sold lots of 115/145 way back when

Bonus question anyone?

[EricJ]

24 minutes ago, cliffy said:

Using Wiki was cheating

Sold lots of 115/145 way back when

Bonus question anyone?

If you mix equal amounts of two different dyed avgas octanes, what color are they?   e.g., if you mix green 100/130 and blue 100UL, what does it look like?

 

[Marauder]

If you mix equal amounts of two different dyed avgas octanes, what color are they?   e.g., if you mix green 100/130 and blue 100UL, what does it look like?
 

Cyan.

Here is a good question. What color of diesel is in a farmer’s truck?


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[bcg]

Cyan.

Here is a good question. What color of diesel is in a farmer’s truck?


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Legally? Clear.

Right now? Probably red. I've got 1200 gallons of red dye on the ranch right now. None on the truck though....yet.

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[Marauder]

Legally? Clear.

Right now? Probably red. I've got 1200 gallons of red dye on the ranch right now. None on the truck though....yet.

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I figured someone knew what I was talking about.


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[EricJ]

2 hours ago, Marauder said:

Cyan.
 

It's actually clear.   The dyes are supposed to cancel, so that you don't get things like mixing 80/87 (red) and 100UL (blue) to make 115/145 (purple).

 

[Dick Denenny]

Found this interesting. Totally side story.  My 23 yo grandson is instucting helicopter a UND having graduated last spring. He's checked out in my 66 M20E but hasn't flown it since last winter. He came home to Spokane so of course we had to go flying and get those three landings in. So he told me that they are going 100%  UL94. They have 123 aircraft and 7 helicopters

[jamesm]

I tend to stick what works. mogas  and others fuel substitutes can contain alcohol and other chemical that can attack seals o-rings and other components  in the fuel systems. Just ask one of the guys who have done tank seal if they want to do it again? do questionable or unknown chemical component in the mogas or other fuel substitute that "should work"  let alone octane rating as others have pointed out. If were a drop in replacement like  GAMI G100 then I would be interested.