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Can one mix some mogas / car petrol into avgas, for emergency use?

What would happen?

Presumably the octane rating would fall, manifesting itself in a higher CHT.

I believe this is fairly widespread in some parts of the world, often using avgas in one wind and the other stuff, for enroute use only, in the other.

Administrator
Shoreham EGKA, United Kingdom

If the plane is approved for Mogas by STC you can mix Avgas and Mogas. I do it all the time in my Warrior.

No STC, otherwise I would not be asking

Also car petrol is not Mogas…

Administrator
Shoreham EGKA, United Kingdom

I have done it a couple of times (use car petrol) to a limited degree, with the SR20 (Continental IO-360, 200hp@2700 RPM, CR 8.5:1) when I flew in the east of Europe.

I don’t worry about octane at all (as long as you use the tank with the blended only for low power cruise). The concern is alcohol and other weird stuff in the fuel.

Hence, I would worry even less with proper Mogas.

Last Edited by boscomantico at 02 Jun 09:24
Mainz (EDFZ) & Egelsbach (EDFE), Germany

You also asked about Mogas, no?

I think if really necessary i’d fly my IO-550 with car fuel, mixed with 50 percent Avgas anyway. I’d use a lower pwr setting and prob not fly above FL100 … but i am pretty sure there would be no problems

Last Edited by Flyer59 at 02 Jun 09:09

I don’t know about Mogas but “sources” tell me a PA28-180 runs very well on african car fuel when alternatives lack.

What would happen?

Absolutely nothing

Presumably the octane rating would fall, manifesting itself in a higher CHT.

I know somebody very well who does this regularly when there is no Avgas. The strategy is always to remove remaining avgas from one wing and top off the other so that there is one wing with pure avgas and then the other wing gets a mix with 95 octane auto fuel. For takeoff and landing, the avgas wing is used and for 65% cruise the mix wing. With a 6 probe EGT/CHT/TIT monitor, not a single degree in CHT difference, no change in power, no sound, nothing is noticed.

BTW: This is with a turbocharged high compression (8.5 :1) Lycoming 540, i.e. the worst possible combination. If you limit this mode of operation to 65% cruise, it works perfectly well. The only drawback is that car fuel stinks much worse than avgas.

Last Edited by achimha at 02 Jun 09:56

What is the difference between car petrol and mogas?

The elephant is the circulation
ENVA ENOP ENMO, Norway

Mogas is usually checked for ethanol content. Our airfield gets it from the standard dealers and has its own equipment. The official name is EN228.

I have mixed AVGAS with up to twenty percent of ULTIMATE 102. With the Lycoming IO 540 Turbo engine I have not noticed any change in the engine running, even CHT and TIT remain the same as with pure AVGAS up to FL 200. The lower lead content in the mixture can have a positive effect on the valve seats and the spark plugs.
There is obviously a difference in the calculation betweeen Octan in AVGAS and in automobile gasoline, thats what I have heard about but I`m not an expert. In the consequence Octan 102 ist maybe only 95 octan for use in aircraft engine.
Which makes me worried is the use of solvent additives in ULTIMATE 102. There may be a risk to seals of a wet tank as well for the fuel lines.
ARAL use Bio-Ether. I do not know the concentration, this is their secret. For that reason I have stopped the experiments. Any advice of the experts is welcome.

Berlin, Germany
54 Posts
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