Mogas in Carbureted O-360 and Impact on Seals

[RVFan671]

I'm starting to do some testing with non-ethanol mogas in my O-360A1A and right now I have 100LL in one tank, mogas in the other. Heard a random snippet from someone that they'd suggest always landing and shutting down on 100LL as to have the carb sitting in 100LL instead of mogas due to seals deteriorating. Wanted to listen from the collective group if this is in fact a risk, or if any seals are at risk, if I just switched to 100% mogas in the future.

I have an MA-4-5 carburetor P/N 10-3878. It was rebuilt by an A&P in 2020 in case that can inform you of what vintage my seals are, although I don't have documentation on the exact seal kit used in the rebuild.

 

[Dan 57]

Same engine, same carb, running on 99% Mogas for the last 4 years, and 50/50 Mogas/Avgas for the other 14 years of it's life.
The engine has always been stopped in the conventional fashion, using whatever gas the fuel selector was on.

The carb never leaked, and was overhauled twice in this period, last time 3 years ago, no ill effect noted.

 

[BH1166]

RVFAN, I believe the info you heard was concerning alcohol/ethanol. As others have done for years with no ill effects or special use, no lead is no issue. Lycoming supports the use of lower octane UL based on compression

 

[jbDC9]

I'm starting to do some testing with non-ethanol mogas in my O-360A1A and right now I have 100LL in one tank, mogas in the other. Heard a random snippet from someone that they'd suggest always landing and shutting down on 100LL as to have the carb sitting in 100LL instead of mogas due to seals deteriorating.

I have the same engine/carb in my RV-8 and use the above listed technique, 100LL in one tank with mogas/avgas mix in the other. The main reason I use this method is that much(most?) of the mogas I use has ethanol in it, so I make sure to land/park it with pure avgas in the carb bowl. No issues with mine after 2100 hours and 3000+ gallons of mogas used.

It sounds like if you can source non-ethanol mogas you wouldn’t need to do anything special to operate, just gas n go. Lucky you!

 

[uk_figs]

0-360 ECI Titan, on long trips I run non ethanol autogas in the left tank and 100LL in the right and take off and land on the right tank to clear the carb as others have suggested. Has been working fine for 14 years and 700+ hours.
Figs

 

[RVFan671]

The main reason I use this method is that much(most?) of the mogas I use has ethanol in it, so I make sure to land/park it with pure avgas in the carb bowl.

Yeah, we've got a number of stations supporting non ethanol premium (some also support regular and plus as well). I would like to run ethanol fuel as well, but I am not sure how to verify if my fuel system seals would handle it. I'll just work toward using the non-ethonol for now since it isn't too far our or my way to fuel up and I'll run it in both tanks.

 

[Dan 57]

In addition to my post above, I've had methanoled gas in my tanks a couple of times, the worst was Mogas from the nearest car station in Scotland...
The only telltale is then having difficulty removing/replacing my fuel caps as the o-rings have swelled.
Disappeared during the next refuel