Fuel Prices

[GAHorn]

Mogas in rural areas are not mandated to have ethanol and I've seen non-ethanol mogas out where I live (in the country.)

BluElder, the mogas is hard on carburetors and their materials. If you burn it regularly and don't allow it to sit it isn't so bad, but regardless it is harder on carbs and fuel system components. (Mogas sitting in my boat, two mowers, a generator and a friend's 150 have ruined those carbs. It eats up the pewter/aluminum and destroys the gaskets, etc.)
Avgas has a much better personality in that regard and it also has a much longer storage life. (Doesn't deteriorate like mogas.)

I'm not trying to start the mogas wars again, I'm just pointing out that mogas isn't as economical as many seem to think it is.

[N2255D]

I'm just pointing out that mogas isn't as economical as many seem to think it is.

Economy has nothing to do with it. It's just another government mandated money maker. (IMHO) It costs more to produce and causes more emissions to manufacture than it eliminates as it is being burned in engines.

[blueldr]

George,

I could'nt agree with you more on the relative stability characteristics
of the two gasolines.

However, in all of my years of experience with the various types automobile gasolines I've used in automobiles, motorcycles, motor scooters, boats (both inboard and outboard powered), and various other gasoline powered pieces of equipment, I've never had a carburetor rot out. This also includes airplanes over the last sixty years. Yes, I know.
We didn't have mogas STCs back then.

If you've had that much trouble with mogas, I'd tend to believe that your heart is just not pure. I've found that some few native Texans are that way. They're rare, but they're there.

Other than that, you seem to be a nice Texas fella!

[hilltop170]

The engine guy who rebuilt my O-300-D showed me some valves from an engine that had been run on 100% unleaded mogas for 200 hours. The valves were all severely but evenly eroded and apperared as if someone had gone crazy lapping them in with abrasive. The engine guy said it was a common occurance with straight mogas users.

Before I bothered to get an STC, I used leaded regular gas for years and hundreds of hours in the O-300-D in the C-170 and O-470-K in my C-180. Both engines went well past TBO and were still in serviceable condition at overhaul.

My C-170 mogas STC states unleaded regular mogas with 87 min octane. I think if I ever use mogas again, it will be mixed 1 part 100LL in 3 parts mogas to get back to the original 1ml/gal lead content of the old 80/87 avgas.

I agree with George, 100LL is getting cheaper all the time compared with mogas. That's one reason why I'm still using it, and I sure like the smell better than mogas. Another reason is mogas degrades faster than 100LL when left in storage whether in cans, tanks, or your airplane. I have heard the degradation starts in as little as 3 months depending on temperature and type of blend, summer or winter.

In engines that I do use mogas in, I either drain or run the engine dry before storage. I have never had problems when I have done this but if I forget or get careless and just don't do it, I have had carb problems and that brown gunk is tough to clean out. I don't want that happening to my plane.

[blueldr]

IMHO (as the saying goes) I think the guy who showed you the "200 hour" mogas valves was either sadly mis informed or full of B.S.

The next time one of these "experts" expounds on the evils of auto fuel, be sure to ask him how much PERSONAL flying experience he has had using same. I've never found one yet that has personally flown enough to develop a problem. It is always someone else, but they know about it.

Tetraethyl lead in gasoline is used ONLY to raise the anti knock level.

It DOES NOT provide any lubrication of the valves.

I've been using mogas ever since the lead was removed and all it has ever done is keep my spark plugs clean. Thats well over a thousand hours on one of my engines, and never a valve problem.

Perhaps you know that the testing fuel used for the EAA Auto Fuel STC was supplied by AMOCO, whose fuel always was unleaded even before it became mandated by law. As a result, I believe the EAA STC calls for unleaded fuel only. The Peterson STC, on the other hand, allowed the use of either leaded or unleaded regular grade mogas.

[cessna170bdriver]

It's a good think they don't burn water, too. A 12 oz. bottle of water is $1. That's about $12 per gallon.

I was reading some magagzine at a doctor's office recently and one of the letters of the editor said that fuel is still "cheap" comparing it to chicken broth at $6/gallon. I'd worry about that if I used 75 gallons of chicken broth every month like I do gasoline (not counting what I put in the airplane).

BTW if you bought gasoline in 12 oz bottles it would most likely be more than $12/gallon (actually $10.67 at $1/bottle).

Miles

[N1277D]

Here is an interesting bit of info, concerning valve lubrication. If we use nothing but 100LL, the primer and fuel selector valve needs to be lubricated with fuel lube. If the lead was a good lubricant, it seems like these two parts would not need lubrication and all those occurances of valve sticking that occured after 100LL was introduced should not have occured. If we add a little MMO, both the primer and fuel selector valve work well and don't seem to bind up. The binding/hard turning of the fuel selector and primer don't seem to happen as often when we run a mix of 100LL and auto fuel.

I've seen O-470s go to 2400 hrs (1500 hrs TBO) on a mixture of auto fuel and 100LL (3 to 1); when they were opened up, hardly any signs of wear.

These engines were certified with an avgas spec that is different than todays avgas specifications. The orginal engine spec clearly indicates to use fuels with less than 0.5 grm lead /gal, compared to the 2 grm lead/gal for 100LL today. I suspect the most important performance aspect of these engines is how it is flown and maintained, rather than the fuel type. eg. change the oil at 25 hrs and use a filter, maintain good ignition and lean to keep combustion temps up so the bromides can scavange the excess lead.

[KMac]

I am not going to tell you I am an engine expert at any level. I know that in auto engines there are differences between the valves and seats in unleaded engines and the valves in engines meant for leaded gas. It has been awhile since I dealt with it but I believe the unleaded valves are titanium or at least some alloy that is less vunerable to wear and does not need lead lubrication.
Too much lead is a problem in car engines too. When I worked at an airport (working through getting my license) I put 120 octane av gas in my '69 camero (with a 12.5/1 compression 327). I mixed it with 91 octane mo gas. I thought it would gain at least 50 horse power! All I got was a stuck valve and a bent chrome-moly pushrod!

[blueldr]

KMac

How do you suppose all those old cars, those that were built before the unleaded fuel mandate, manage to keep running all these years ?

[hilltop170]

I use 100LL in my 1950 Pontiac with a 455 HO engine with 10.5:1 compression. Runs great, does not knock, and no problems if it sits awhile. I have to fill it up at night so the airport manager doesn't see it.

[GAHorn]

... The binding/hard turning of the fuel selector and primer don't seem to happen as often when we run a mix of 100LL and auto fuel.
... and lean to keep combustion temps up so the bromides can scavange the excess lead.

The binding, etc is worsened by the use of mogas. Mogas is harsh on fuel system components and most mogas also has alcohol which further complicates the issues for corrosion-endangered components like primers and fuel valves.


Yep on the leaning...primarily to reduce the amount of leaded fuel consumed and therefore reduce the exposure to lead. Lead is bad for engines. Good for octane.... bad for engines. The ideal fuel for low compression engines like ours is unleaded avgas. (Preferably at twenty-five cents per gallon.)
Since we have to deal with lead in our avgas.... we should scavenge as much out as we can. The bromides in autofuel no longer exist. Avgas has insufficient scavengers. TCP is the only approved available and I recommend it highly (in whatever form you can get it....Alcor or Decalin.)

I'm about ready to make my own. (But a HUGE THANKS to Richard Pulley for bringing me a whole gallon of the stuff on Turkey Day!)

You guys oughtta see his POTATO GUN! That's a WILD TOY!

[N1277D]

We disagree, our experience is that the binding is worse with pure 100LL. It is a dry fuel that leaves deposits, leading to binding. In my opinon the 100LL specification needs rewritten, taking advantage of the significant progress that has been made in the unleaded fuel technology.

The avgas spec primarly provides for low vapor pressure for high altitude performance and adequate anti knock properties. It has not gone through the continual improvements that have occured with the unleaded base stocks.

Most low compression aero engines, do not need the ability to operate at high altitudes/high temperatures and do not need the anti-knock properties found in the 100 LL av gas specification. Most of these engines were designed before there was an av gas specification.

When highly leaded fuels were introduced there were significant problems with valve sticking in these engines, significant combustion chamber deposit buildups, stuck rings and reduced TBOs.

All gasolines are a mixture of varous hydrocarbons including av gas. The avgas spec provides fuel properties designed to get high performance piston aircraft up to the flight levels. Avgas needs varous additives like bromides to scavage the combustion deposits (lead). The concentrations of bromides are kept low since they are aggressive, (cause corrosion) the result being the buildup of lead deposits in low compression engines. To help eliminate these problems, in low compression engines one needs to lean, keep the combustion temperature up and ensure that the ignition system is close to perfect as you can achieve.

It is well known that unleaded gasoline base stocks have the correct range of properties to function as an avgas for low compression aero engines. In addition these fuels provide other properties, like deposit free operation and better exhaust properties (more enviromentally friendly).

[GAHorn]

We disagree, our experience is that the binding is worse with pure 100LL. It is a dry fuel.... ).

Mogas has alcohol. Nothing is more "dry" than that. (And who is "We"?)

that leaves deposits, ).

... all fuels leave deposits including mogas.

In my opinon the 100LL specification needs rewritten, taking advantage of the significant progress that has been made in the unleaded fuel technology.).

The specification for 100LL doesn't need to be re-written. Another fuel entirely needs to be developed and supplied. But it's unlikely to happen because most corporate piston aircraft need 100 octane fuel, and it's the corporate/business/gov't airplanes which are the most profitable to the avgas suppliers.

The avgas spec primarly provides for low vapor pressure for high altitude performance and adequate anti knock properties. It has not gone through the continual improvements that have occured with the unleaded base stocks.).

There is no "improvement" in "unleaded base stocks" applicable to mogas that is not already applicable to avgas.

Most low compression aero engines, do not need the ability to operate at high altitudes/high temperatures and do not need the anti-knock properties found in the 100 LL av gas specification.).

Yes that is true. But most fuel suppliers do not consider it economically viable to supply more than one fuel-fits-all avgas. I just wish they'd let us select whether or not we want lead at the pump!

Most of these engines were designed before there was an av gas specification. ).

That is not correct. There have been aviation fuel specifications since the 1920's. Modern auto engines have been under continuous engineering improvement to burn modern auto fuels. No aviation engine mfr has approved mogas for their engines and therefore none of them have made any engineering accomodations for the use of mogas. Perhaps the best reason not to use it.

When highly leaded fuels were introduced there were significant problems with valve sticking in these engines, significant combustion chamber deposit buildups, stuck rings and reduced TBOs.).

And those issues have been addressed by changes in engine valve designs. There have been no "reduced TBO's". In fact there have been increases in many aviation engine TBO's. There has been no increase in "significant combustion chamber deposit buildups" which have any adverse effects on the combustion chambers. That sounds like an ad campaign worthy of "putting a Tiger in your tank."

All gasolines are a mixture of varous hydrocarbons including av gas. The avgas spec provides fuel properties designed to get high performance piston aircraft up to the flight levels. Avgas needs varous additives like bromides to scavage the combustion deposits (lead). The concentrations of bromides are kept low since they are aggressive, (cause corrosion) the result being the buildup of lead deposits in low compression engines. To help eliminate these problems, in low compression engines one needs to lean, keep the combustion temperature up and ensure that the ignition system is close to perfect as you can achieve. ).

And use TCP.

It is well known that unleaded gasoline base stocks have the correct range of properties to function as an avgas for low compression aero engines. In addition these fuels provide other properties, like deposit free operation....

With regard to the "correct range of properties to function as avgas". - Absolutely incorrect. Virtually none of the latest mogas forumulations meet any of the mogas STC's approved for airplanes. (Regarding the "deposts" - You meant no lead deposits perhaps?)

and better exhaust properties (more enviromentally friendly).

But don't pipe it into your home.

[blueldr]

It seems strange that the rest of the non flying world has so little trouble with mogas eating up the "aluminum,pewter and gaskets" in all manner of machinery and equipment. Especially automobiles.

As for the guy with the "150", his carburetor must have been something other than a normal Marvel-Schebler. I hasn't bothered mine in all these years. Not even the gaskets.

Like I said, most of the "experts" have very likely had absolutely no personal flying experience using mogas in airplanes.

[GAHorn]

I don't claim to be "expert". I only know what it did to my equipment and my Aeronca with a Marvel carb.
The "rest of the world" is not without those who have had similar problems with mogas. Perhaps if we all had the exact same formulations of mogas that haven't caused trouble, and if perhaps we all could be assured that mogas formulations wouldn't change with region, seasons, suppliers and transporters, this wouldn't be a subject with such widely varying experiences.
I use what my airframe and engine manufacturers specify.