Leaded Aviation Fuel?

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seaweed

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Eastern Shore, MD
Any advantage of using leaded aviation fuel in my little 1992 Johnson 3hp motor as opposed to just using regular non-ethanol? I can get both here on the eastern shore of MD, but wondering if it's worth splurging on aviation fuel? I believe it has an octane rating in the high 90's, but don't hold me to that.

Thanks! Before I joined, I absorbed a ton of excellent info from you fellas!
 
no. counter productive. more octane equals slower burn, less power, less efficiency. you dont need lead to lubricate and cushion the valves. run ethanol with stabil or star brite and call it a day as long as it doesnt attack your fuel system. note: if you use the gas in your tank, and use star brite, you will have no trouble. if you take a long time to use a tank full, dont fill the tank as full. the trick is to cycle the fuel in the tank before it goes bad and attacks your plastics and rubber.
 
seaweed said:
Any advantage of using leaded aviation fuel in my little 1992 Johnson 3hp motor as opposed to just using regular non-ethanol?

No, don't use it. What you will likely get is 100LL, which contains 3x the tetraethyl lead that automotive leaded pump gas used to have. All it will do is foul your spark plugs, it will stick the top ring on the piston and score the cylinder, and you will get a noticeable drop in power without advancing the timing. Remember that piston airplane engines that use it use special aviation oils that cost $10/qt and are formulated to help prevent lead fouling of the top piston ring, and have two spark plugs per cylinder because the mixture in the combustion chamber needs to be lit on both sides to shorten the burn time.

Plus the airport likely won't sell it you anyway unless you own an aircraft because it's illegal to use it in anything but an aircraft engine.
 
I used to use it in my1992 johnson 3 hp up until it got put away for a few seasons. I used it in everything (on the advice of a duh-canic)....but on the airport on kent island, md, you just walk up, set your tanks down, put in a credit card and pump away. Never had anyone tell me otherwise.
 
Here in Pa. you can legally pump it into containers for "OFFROAD USE" since it doesn't have a highway tax included in the price. I don't know about boat motors, but I do know that the 100 LL works pretty good in my 427!
 
overboard said:
Here in Pa. you can legally pump it into containers for "OFFROAD USE" since it doesn't have a highway tax included in the price. I don't know about boat motors, but I do know that the 100 LL works pretty good in my 427!

whats the price per gallon ?
 
poorthang said:
overboard said:
Here in Pa. you can legally pump it into containers for "OFFROAD USE" since it doesn't have a highway tax included in the price. I don't know about boat motors, but I do know that the 100 LL works pretty good in my 427!

whats the price per gallon ?

I haven't bought it in awhile so I don't know, last time I talked to someone about it I think they said it was over $6.00 a gal. If I wanted max performance, with timing advanced, etc., I would probably have to run it all the time, but with the motor tuned back to factory specs. and mostly a garage queen now, I can get away with just running high test pump gas, usually Sunoco. I think when I first put the hi test av gas in the car it was 110 octane, then they dropped it to 100 where it's been for quite a while.
 
FWIW, I just stopped at the park district airport & filled up the boat (ethanol free, 91 octane gas) this afternoon.


Screenshot_20220628-182659_Brave.jpg
 
KMixson said:
The only advantage would be your gas would be a pretty shade of blue until you poured in the two cycle oil. That is all.

It's a bigger difference than that. Avgas is formulated to burn slow with a low vapor pressure to prevent vapor lock at high altitudes. It is formulated for low compression air-cooled engines that need lead for valve seat lubrication, and that run 30 deg BTDC fixed timing with dual magnetos. Air-cooled aircraft piston engines are 1940's technology, and they haven't changed in that amount of time because it is incredibly expensive to get certification for any newer modern engine designs. So you buy a brand new Cessna 172 and the Lycoming IO-360 in that airplane is the same engine that was sold in 1955, and it still has the same 2,000 hr TBO. Which is not too good, considering that most modern automotive engines will run at least 6,000 hrs to overhaul.

Aircraft piston engines are some of the lowest technology engines still in common use, and the only reason 100LL still exists is because there is no replacement for the engines in airplanes that still require it.

100LL is not "good gas" like many think it is. Using the R+M/2 method they use at the pump for automotive gas, 100LL is somewhere between 80-85 octane.
 
I believe if you check you will find out most 100LL is a minimum of 99 octane. My best friend is a distributor to the local airport here and that is the minimum they have.
 
There's been lawsuits in California over FBO's selling 100LL because the lead in the engine exhaust settles in the residential neighborhoods close to airports.

https://generalaviationnews.com/2014/12/17/settlement-reached-in-california-avgas-lawsuit/

The phase-out of 100LL in general aviation began when I was still flying commercially. Commercial aviation no longer uses piston engines except for some remote areas in Canada and Alaska where commercial single or twin piston airplanes are still used for commuter airlines and remote bush services. So the phase-out only basically affects general aviation for recreational use.

https://www.aopa.org/news-and-media/all-news/2022/february/pilot/alternative-fuels-for-all
 
nccatfisher said:
I believe if you check you will find out most 100LL is a minimum of 99 octane. My best friend is a distributor to the local airport here and that is the minimum they have.

Sorry, but totally different rating. Octane is not octane. Octane gets its name from 2,2,4-trimethylpentane, which is an iso-octane. This iso-octane has been assigned the reference value of 100 for testing purposes. The normal heptane (C7H16) molecule is the 0 octane reference fuel.

There is two different ratings, RON, and MON. 100LL uses the RON method. Automotive pump gas uses the RON+MON/2 method, which is the average of motor octane vs research octane. So while they can call 100LL 100 octane for aviation purposes, for automotive purposes it is the equivalent of the "mountain gas" they sell in the western mountain states. Only difference is, it contains a LOT of lead - 3x what the old "ethyl" leaded premium automotive gas used to have in the 60's.

Do not use it in your outboard - it will mechanically damage the engine due to the amount of lead in it. And I'm telling you that as a commercial pilot (now retired) and I also hold a A&P. Been working on aircraft engines for 40 years. The spark plugs in an aviation piston engine barely last 100hrs due to lead fouling. And the ignition systems used on piston aircraft engines are way hotter than what you have on your outboard. They have to be to fire the plugs with all the lead, and we can't abrasive-blast aviation engine spark plugs to clean them - it's illegal. And it costs $270 to put a new set of spark plugs in a typical four-cylinder opposed aircraft engine. If you think boats are expensive, try airplanes.
 
C&K said:
nccatfisher said:
I believe if you check you will find out most 100LL is a minimum of 99 octane. My best friend is a distributor to the local airport here and that is the minimum they have.

Sorry, but totally different rating. Octane is not octane. Octane gets its name from 2,2,4-trimethylpentane, which is an iso-octane. This iso-octane has been assigned the reference value of 100 for testing purposes. The normal heptane (C7H16) molecule is the 0 octane reference fuel.

There is two different ratings, RON, and MON. 100LL uses the RON method. Automotive pump gas uses the RON+MON/2 method, which is the average of motor octane vs research octane. So while they can call 100LL 100 octane for aviation purposes, for automotive purposes it is the equivalent of the "mountain gas" they sell in the western mountain states. Only difference is, it contains a LOT of lead - 3x what the old "ethyl" leaded premium automotive gas used to have in the 60's.

Do not use it in your outboard - it will mechanically damage the engine due to the amount of lead in it. And I'm telling you that as a commercial pilot (now retired) and I also hold a A&P. Been working on aircraft engines for 40 years. The spark plugs in an aviation piston engine barely last 100hrs due to lead fouling. And the ignition systems used on piston aircraft engines are way hotter than what you have on your outboard. They have to be to fire the plugs with all the lead, and we can't abrasive-blast aviation engine spark plugs to clean them - it's illegal. And it costs $270 to put a new set of spark plugs in a typical four-cylinder opposed aircraft engine. If you think boats are expensive, try airplanes.


I'm going to admit the octane discussion is way over my head. But, I do have a question. If the leaded octane fuel is such a big maintenance issue, why does aviation gaso have so much lead in it?
 
LDUBS said:
I'm going to admit the octane discussion is way over my head. But, I do have a question. If the leaded octane fuel is such a big maintenance issue, why does aviation gaso have so much lead in it?

The lead is to keep the valves seats protected when running in a lean condition. On piston driven airplanes, you have control over the lean or rich mixtures of the fuel to the engines. Lean is hot and rich is cool.
 
LDUBS said:
I'm going to admit the octane discussion is way over my head. But, I do have a question. If the leaded octane fuel is such a big maintenance issue, why does aviation gaso have so much lead in it?

In aircraft engines the valve seats and valve material can't be changed without getting a STC (Supplemental Type Certificate), which is very expensive to get. So the same materials are used for replacement parts at overhaul as what the engine was originally certified with. Those certifications (called a Type Certificate) were obtained back in the 40's and 50's when the engine was originally designed and certified.

So, unfortunately, they still require the lead for valve seat lubrication, and these are air-cooled engines that run cylinder head temps of 435-450F at full power, 375 at normal cruise power. Lubricating oils formulated for automotive engines can't withstand those kinds of temperatures, and neither can automotive fuels - vapor pressure is too high with automotive fuels. There are STC's you can get for some engines (like the Continental O-200) to allow use of automotive gasoline. But the STC limits the altitude the aircraft can be operated at, and shortens the TBO (Time Between Overhaul).

The general aviation industry is badly in need of more modern engine designs that can use unleaded fuels. But it is too expensive to get the certifications for it, and the general aviation market can't bear the cost. Commercial aviation switched to turbine power long ago. But general aviation can't bear the cost of turboshaft engines either - a typical small Pratt&Whitney Canada PT6 engine costs $1.1 million, where the piston equivalent costs ~$80,000.

Running 100LL in your outboard at the cold temperatures that outboard engines run at will only cause extreme lead/carbon buildup on spark plugs, piston crown, combustion chamber head and exhaust ports. It will build up in the top ring land and seize the ring, resulting in a scored cylinder.

Unfortunately, this also happens to aircraft engines. Take like a Seneca V with twin turbocharged Continental TSIO-360's, the TBO is 1,800 hrs. But the engines will have to be "topped" at around 1,000 hrs, meaning the cylinders and pistons are replaced with new to make it to TBO, without removing the engines from the airframe. The cost to "top" a pair of TSIO-360's is around $37,000, and major overhaul is ~$57,000 apiece. The cost of the airplane is $1.15 million new for a 2022 model. This is just a light personal twin. If they replaced those two piston engines with a couple small PT6 turbines, the cost of the airplane would be over $3 million. Turbine powered GA personal airplanes are very expensive. A single-engine TBM940 is a $4.5 million dollar airplane and it costs $744/hr to stick the key in the switch and start it.
https://air.one/aircraft-showroom/daher-tbm-940

This is an accepted part of the cost of flying airplanes - nothing about them is cheap. It's not an accepted part of operating outboard motors.

Some people still do run avgas in certain 1960's muscle car engines. But if you put that engine on a dyno and compare 100LL avgas to Sunoco Optima 95 race gas, you'll find you get way more power with the race gas. 100LL avgas is 112,387 BTU/gallon (18,700 BTU/lb). The old MTBE formulated automotive gasoline was 124,880 BTU/gallon. E10 87 regular automotive gas is 114,100 BTU/gallon. So basically, 100LL avgas does not even have the energy content per gallon that today's regular E10 87 octane pump gas has.
 
The aviation gasoline in common use before 100LL was Avgas 80. It used motor octane rating (MON) instead of RON. It had slightly over twice the lead content of 100LL. Its use was banned by the EPA in 2009 when the last refiner of Avgas 80 went out of business. Everybody had to switch to 100LL, and 100LL is being phased out now in favor of UL91. Nobody in the general aviation business really knows what the FAA is gonna do regarding certification of older engines for UL91. Shorten the TBO? Simply ground them and declare them obsolete? Limit them to 6,000 ft and 20 deg C like they do with automotive gas STC's? Nobody knows.
 
C&K said:
In aircraft engines the valve seats and valve material can't be changed without getting a STC (Supplemental Type Certificate), which is very expensive to get. So the same materials are used for replacement parts at overhaul as what the engine was originally certified with. Those certifications (called a Type Certificate) were obtained back in the 40's and 50's when the engine was originally designed and certified.

So, unfortunately, they still require the lead for valve seat lubrication, and these are air-cooled engines that run cylinder head temps of 435-450F at full power, 375 at normal cruise power. Lubricating oils formulated for automotive engines can't withstand those kinds of temperatures, and neither can automotive fuels - vapor pressure is too high with automotive fuels. There are STC's you can get for some engines (like the Continental O-200) to allow use of automotive gasoline. But the STC limits the altitude the aircraft can be operated at, and shortens the TBO (Time Between Overhaul).

KMixson said:
The lead is to keep the valves seats protected when running in a lean condition. On piston driven airplanes, you have control over the lean or rich mixtures of the fuel to the engines. Lean is hot and rich is cool.


Thanks guys. I definitely learned something new today.
 

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