mogas

[treetopflyer]

does anybody know about using auto gas in a M5 235 C. I talked to petersen and he said that the feds had required another detonation test to allow the STC process to continue, and it was not worthe the money he would have to spend.So no STC at this time Of course I would never actually use fuel that is 2/3 the price of 100LL nor would I ever do anything contrary to my Uncle aka FAA. r

[maules.com]

The Lyc. O540 J1A5D in the M5 was never Stc'd for mogas in the Maule.
In the days before ethanol addition to most mogas today, I have heard say mogas was used with a mix of Marvel mystery oil, rumours mind you.
I understand that a number of mogas Stc's do not apply if amounts of ethanol are present.

[RobBurson]

Hello treetopflyer: I have a M7 235C B4B5 Lycoming. Lo compression. Mine is STC for mogas. First off Lycoming doesn't like mogas even with STC. I have the Peterson STC. I have never used mogas in it. The main thing seems to be vapor locking in warm temps. Part of the kit is a different fuel pump. Less prone to vapor locking. More vents with ducting to areas that need the cooling. Lots of instructions on what to watch for, and what to do if this or that happens. The fuel must be tested for alcohol. Alcohol is a BIG NO NO! I hope this helps. Regards...Rob

[TomD]

I think if you look on your engine casing closely enough you will find a placard with the required octane and compression ratio.

As much as I would like to have a mogas or boat gas option on my M5 I am thinking we are stuck w/ 100LL. The "B" version engine is the only one w/ a mogas STC as far as I can tell.

I have heard of people putting mogas or boatgas in one tank in a pinch and taking off w/ 100LL and switching to mogas at cruise. This minimizes detonation which causes those annoying holes in the pistons.

TD

[eskers]

Jeremy

Just going through the old threads on MOGAS. Is the Lycoming O540 J1A5D a low compression engine even though it has not beem stced yet?

Thanks

Eskers

[a64pilot]

I think only the "B" is low compression. You can tell for sure by the max RPM though, the high compression motors hit 235 HP at a lower RPM than the low compression ones do.
I feel real sure that if you retard your timing 5 degrees and restrict manifold pressure to 25" you would be fine even in the high compression fuel injected motors. I have seen and know people with experimental aircraft that are doing exactly that.
You will not always hear detonation though, entirely possible your first indication of detonation will be when you lose a cylinder, pre-ignition, you will hear, but that is not detonation. So, it is a gamble.
I have a source of alcohol free Mogas for my C-85 in my little 140 and while I am sure alcohol isn't good, I have not heard of one single accident attributed to it's use, and I know many people who do not test their fuel for it, so I know thousands of airplanes are flying around with E10 in them.

[maules.com]

The B carb engine is low comp 7.2 and 2575 rpm for 235hp and J carb engine comp is 8.5 at 2400rpm for 235hp.
The case and crank are heavier in the higher rpm engines generally speaking.

[aero101]

There are other problems with mogas as well... Most of it available anymore throughout the U.S. does not meet the legal requirements of the STC in the first place due to additives. It eats up O-rings and hose such as whats installed on your sump drains. It has nowhere near the storage life of avgas and will rapidly deteriorate depending upon time of year / area purchased. And on top of it all, in cold dense air it doesn't make the power of 100LL, as I've seen over 200RPM difference in static thrust on an O-320 demonstrated. I feel if you want to run mogas, get rid of your airplane and buy another car!!

[a64pilot]

Depends on the engine. Both the little C-85 and the 1340 seem perfectly happy with it, but both are relatively low compression engines, even if the 1340 is supercharged. I believe the min. octane requirement for both is 73.
I believe any engine that back in the day ran fine on 80/87 octane Avgas, is happy with autofuel.

[eskers]

In a bind, stuck somewhere in the NWT, can higher octane (premium) gas be used in the O540 J1A5D for a short time?

Cheers

[Mountain Doctor]

I'm no expert but as I understand it the problems would be associated with detonation/preignition at higher power setting so I bet you'd be fine at lower power. Say 75% for takeoff and climb, 60% for cruise but it's a potentially expensive experiment.

[a64pilot]

Well, I can tell you for a fact that an IO-540W1A5D will run just fine on 93 Octane Amoco Mogas on a 100 deg day at 30" and 2450 RPM and sea-level up to 11,500 ft, and cruise there just fine for four hours. RPM was reduced to 2400 after TO and throttle left full open for the flight until time for descent.
But when shut down to re-fuel with 100LL on a hot day, it started fine five min. later, but vapor locked for about 1 min. Ran a little rough with the fuel flow indicator (pressure gauge) fluctuating all over the place because of the intermittent vapor. Now did it quit vapor locking because of cool fuel from the tank, or because it got to the 100LL?
Turning on the electric fuel pump did not reduce the vapor lock either.
So, I can deduce maybe vapor lock may be the real issue for some engines on Mogas?
But it was very hot, South Florida and I think shut down just long enough to heat soak everything, but not long enough to begin cooling either.