Fuel Question

[srf471]

I recently purchased a L2M with a C-85-12 engine. The previous owner used a mixed concoction of 25% 100LL, 75% 87 Octane MoGas, and Marvel Mysrtery Oil (4oz per 10 gallons).
I'm curious, what do you guys use for fuel in a C-85. Is this mixture 1) correct 2) necessary?
Any advice would be greatly appreciated.

Nick
N58075

[Jim Hartley]

Re: Fuel Question

Same mixture for my 85. Eliminated difficult hot starts and carbon particles in the plugs. With the 100LL the engine receives lead for valve lubrication. The MMO...? It is a fine grade machine oil with solvent properties and the smell helps cut the smell of car gas,somewhat.

jim

[Goneflyin]

Re: Fuel Question

I have a 12d with a 65 but when I first got the plane I ran straight mogas and after 20 hrs I had an exhaust valve seat start leaking because it moved. I Had it fixed and about 40hr later same thing on a different cylinder.
I started running 5gal of mogas to 1 gal 100, I only do that combo cause it's easy, but 400 hrs later no leaky valves.
When I first had the problem I read somewhere( maybe EAA) that the car gas runs hotter and the exhaust valve"sticks" to the seat so on the next cycle it tries to pick the seat up when the valve opens. Keeping a little lead in it seems to work in this engine and the plugs usually start first flip with close to 500 hrs on them. Every motors different though.

Bill

[flyguy]

Re: Fuel Question

The word years ago from hot rod engine builders was the the lead coats the valve seat lubricating it and keeping it from erroding and burning (oxidizing was the word used.)
What I heard was that running some leaded thru initally would put enough lead on the seats to protect them when using unleaded later.
Personally I think using the combo as mentioned by the guys above covers all the bases.
Darryl

[gusc]

Re: Fuel Question

The mogas/avgas issue was put to bed by the EAA in '81 or '82 as I remember. They put hundreds of hours on a C-150 w/O-200 and had absolutely no problems.

Just because an engine has valve or whatever problems while running mogas does not mean the gas caused the problem.

Most of the hangar talk you hear about the perils of mogas is just that, a lot of undocumented bull.

If anyone wants it I have a copy of a letter written in answer to one of the naysayers by an engineer with EAA who actually knows what he is talking about. I am not an EAA member.

[flyguy]

Re: Fuel Question

I keep hearing about people using auto gas. Did I read the EAA wrong that fuel with alcohol in it is not covered by their STC? Is there a STC that allows it?
I understand that adding ethanol to auto fuel is federally mandated throughout the U.S. All the gas I have tested in California in the last year or so tests positive for alcohol.
A guy I know operates several airplanes on mogas. It is only 5% he says.
What is the lastest on this.

[paulp]

Re: Fuel Question

Howdy Tribe,

Peterson aviation recommends, on an overhauled engine, that the first 100 hrs should utilize 100LL. Then go to mogas. They say the lead coats the valves.

I have a C-85 with the 0200 stc and I can't find an STC for mogas!!!

[gusc]

Re: Fuel Question

The way I remember it alcohol is to be avoided. Not sure about the reason but believe it was a corrosion problem plus maybe the alcohol caused a vapor lock problem, less sure about that part.

This stuff happened a long time ago!!

[mhorowit]

Re: Fuel Question

The alcohol has an effect on the rubber components - Mike

[Robert Lees]

Re: Fuel Question

I had an interesting conversation a year or so ago, with a guy who owns a 1936 Bentley Open Tourer, 400hp V8 engine. I asked him how he overcame the problem of leaded car fuel not being available any more in the UK.

He said: "My boy, when this engine was built, there was no lead in car fuel....so I run it now on unleaded, as I always have" (He was about 85 years old).

Personally, I am not convinced of the lead/lubrication story, although I do personally believe that alcohol and similar additives do more harm that is understood.

Despite the Bentley story above, and that I indeed fly a similar vintage (but lesser horsepower) engine, I have always used 100LL (which has more lead in it than leaded autofuel). But 100LL has no Alcohol or stuff in it. 100LL works just fine, although I have had the Stellite valves installed.

Just my opinion.

[Karl Rigdon]

Re: Fuel Question

Does anyone know the BTU content of alcohol? Gasoline is about 120,000 BTU per gallon. #2 fuel is as I recall about 140,000 BTU per gallon. LP is 92,500 per gal. Between what I feel is the lower BTU per gallon for alcohol and the cost to raise the crop and make the alcohol it is at least a zero sum gain. To gain any advantage from alocohol you need a much higher compression.
Keep in mind the A65 is rated for 73 octane fuel that I am sure was unleaded.
I hear stories there were old time mechanics that were worried when they added the tetra ethel lead to the gas. As was stated in other post it did extend valve life.
I remember some guys thinking using 115/145 was going to give their cars more power. All it got them was fouled spark plugs.

[gusc]

Re: Fuel Question

Actually, 100LL has eight times as much lead as 80 Oct Avgas so it has many more times as much as unleaded Mogas, exactly how much more I don't know.
Octane rating is not much of an issue since these engines were designed to operate on 73 Octane.


" I have always used 100LL (which has more lead in it than leaded autofuel). But 100LL has no Alcohol or stuff in it. 100LL works just fine, although I have had the Stellite valves installed.

Just my opinion.[/QUOTE]

[jgerard]

Re: Fuel Question

Adding lead to fuel increases the octane of the fuel. Lubrication is only a side affect/bennifit.

Jason
N43643

[M Towsley]

Re: Fuel Question

Flyguy,

I have found, (locally), that Sams Club carries fuel without alcohol in it. Both regular and premium. I test every batch, though. It is law that they mark the pumps if the fuel contains alcohol. But that does not mean they put the sticker in a noticeable place, look everywhere on the pump.......but test it anyway!!! Most of the majors, BP, (Amoco), Shell, (Equilon or Equiva depending on region), etc., have no alcohol in their premium fuels. I have also found FS stores carry alcohol free fuel. Again, check every batch. I utilize Peterson's fuel tester, takes only a few minutes to confirm. Good luck.

Marty
N95275

[flyguy]

Re: Fuel Question

Marty,
Thanks for the info and incouragement, but California mogas, like most things here, is out there in woohoo land. The bureaucrats put MTBE in and then found it was poisioning everything, so they took it out. Then the congress came up with the idea of subsidizing the corn-growning states and California of course said, "Yeah, great idea, lets put some other crap in the gas."
Anytime you get non-technical people making technical decisions eveything goes to S**T. Witness 14 dead astronauts.
Car gas is so expensive here that it isn't worth the trouble anyway.
Darryl