MOGAS and Muffler Issues

D

DwayneSmithUSMC

Pre-Flight
Joined
Jul 23, 2014
Messages
91
Location
Virginia
Display Name
Display name:
DwayneSmithUSMC
I own a Cherokee 235 and have been buring MOGAS for the past 4-5 years. In that time I've had to have my muffler overhauled going on 3 times, each time costing me a few hundred dollars (not much when all things considered). I've had absolutely ZERO engine issues running MOGAS.

This time my mechanic called a muffler shop and was told that high performance planes who burn MOGAS tend to blow out the flame tubes on mufflers if they lean the mixture at all because it burns much hotter than 100LL. Their suggestion was to not lean at all when using MOGAS. My response was to question how can I run full rich without burning 20+GPH.

Has anyone had muffler issues with running MOGAS? If so, how did you correct for that and still run MOGAS.
 
I haven't burned MOGAS since they started putting booze in it, can't get the unadulterated stuff at any airport within a hundred miles of me. Of course the obvious answer is "don't run Mogas", but my guess is that's not what you want to hear. I didn't even know the Cherokee 235 had an STC for Mogas.
 
steingar said:
I haven't burned MOGAS since they started putting booze in it, can't get the unadulterated stuff at any airport within a hundred miles of me. Of course the obvious answer is "don't run Mogas", but my guess is that's not what you want to hear. I didn't even know the Cherokee 235 had an STC for Mogas.
Click to expand...

I'm assuming you mean ethanol. Yes, there's an ethanol-free gas station near me. As far as your answer is concerned, yes, it's not what I'm trying to hear as my question is for people who have experienced this and how they were able to still use MOGAS and correct for the muffler issue. If I can't find any answers, the obvious solution is to switch back to 100LL but I'd rather not. What I'll likely do is some experimentation with leaning and try to figure out when the muffler issues arise. That way I can find the right mixture settings to correct for the issue.
 
Heat alone may not be the issue. I have attributed internal distortion to heating and COOLING. Are you doing a lot of pattern work or touch n go’s ?

Are affected mufflers all the same brand?
 
Magman said:
Heat alone may not be the issue. I have attributed internal distortion to heating and COOLING. Are you doing a lot of pattern work or touch n go’s ?

Are affected mufflers all the same brand?
Click to expand...
Good morning. Yes, the affected mufflers were the same brand. I mostly do x-country flying at ROP.
 
Clip4 said:
There are different compounds in unleaded fuel compared to 100LL that may be more corrosive. I doubt the issue is heat.
Click to expand...
That makes sense. Do you know of a type of muffler that works better with MOGAS?
 
Mogas does not burn hotter than 100LL. If it has ethanol (which there shouldn't be/must not be if you're burning it in a Lycoming under an STC) it will run leaner. For untainted mogas, the main difference is its lower octane, which shouldn't be an issue in an engine designed for 80/87.
 
Are there any STCs for an unmuffled exhaust? It’s nice flying an Experimental - Vetterman exhaust, basically headers and straight pipes.
 
I would think that whoever you got the STC from would have done some testing and could tell you if the exhaust temperatures are actually higher with mogas as compared to 100LL.
 
Capt. Geoffrey Thorpe said:
I would think that whoever you got the STC from would have done some testing and could tell you if the exhaust temperatures are actually higher with mogas as compared to 100LL.
Click to expand...
I would think so too, which leads me to believe that the likely issue is the muffler itself and not the MOGAS.
 
I’ve been running a Powerflow with Mogas and 94UL at lean of peak consistently. No issues. 1450 degree egt.
 
DwayneSmithUSMC said:
Thanks for the info. I'm pretty sure at this point it must be the muffler itself.
Click to expand...
Is there a power flow exhaust available for your plane?
The power flow exhaust on my C172 0-320 does not have a muffler to rust or crack. Just 4 tuned pipes into a collector.
 
Last edited:
DwayneSmithUSMC said:
Good morning. Yes, the affected mufflers were the same brand. I mostly do x-country flying at ROP.
Click to expand...

Maybe how far ROP vs LOP makes a difference. As well, your engine monitoring technology and accuracy? Just throwing wild thoughts out.
 
Clip4 said:
There are different compounds in unleaded fuel compared to 100LL that may be more corrosive. I doubt the issue is heat.
Click to expand...
Which compounds are those that are more corrosive?

To raise the octane rating in Mogas, they have more alkenes and aromatic compounds such as toluene and various xylenes, and those aren't corrosive. The OP mentioned he isn't using gas containing ethanol.
 
DwayneSmithUSMC said:
I own a Cherokee 235 and have been buring MOGAS for the past 4-5 years. In that time I've had to have my muffler overhauled going on 3 times, each time costing me a few hundred dollars (not much when all things considered). I've had absolutely ZERO engine issues running MOGAS.

This time my mechanic called a muffler shop and was told that high performance planes who burn MOGAS tend to blow out the flame tubes on mufflers if they lean the mixture at all because it burns much hotter than 100LL. Their suggestion was to not lean at all when using MOGAS. My response was to question how can I run full rich without burning 20+GPH.

Has anyone had muffler issues with running MOGAS? If so, how did you correct for that and still run MOGAS.
Click to expand...
Do you have an engine monitor? Close GAMI spread? How far ROP or LOP do you cruise?

the gasoline formulation isn't causing this... your operating conditions might be.

Paul
 
Many turbine engines are followed in “ cycles “ of HOT/COLD.

1/2 hour or 12 hours makes little difference.

Sort of like a sauna and roll in the snow?
 
Our 172M burned out the flame tubes about every 400 hrs when it first ran on 80 octane way back then, and again when it ran for about 1400 hrs more on MoGas. Our mechanics would only allow the flame tubes to be come so warped on annual.

The purpose of fuel is to provide heat. There is no reason for MoGas to be damaging your muffler. Your mechanic is just being careful - for you.
 
I have never seen a detectable difference in component longevity after running many hours on both unleaded and leaded gasoline. I suspect the reason for your failures are related to the exhaust shop and the material selection they’re making.

It continues to surprise me what gets blamed on alternative fuels.
 
My experience with flame cones on Pipers has been that they blow out after about 5min regardless; I doubt the fuel is the issue. The solution is to find an IA who understands this and isn't prone to make you rebuild your mufflers every year over a useless part.
 
Cap'n Jack said:
To raise the octane rating in Mogas, they have more alkenes and aromatic compounds such as toluene and various xylenes, and those aren't corrosive. The OP mentioned he isn't using gas containing ethanol.
Click to expand...

Except 94UL is 100LL without the lead. And higher octane than MOGAS.
 
My local IA has a 235 in the shop with exhaust problems.

His take is that the exhaust systems are not as good as they were, both in material and construction.
 
You must log in or register to reply here.
Back
Top