?Sticking Valve or Carb Ice?

[Bruce Fenstermacher]

Mogas is $4.17 (91 octane) and avgas is $5.51 here (KLVK). Ah CA...worth every penny

http://www.cessna170.org/forums/viewtop ... 214#p99214

There you go. MOGAS is currently $3.35 and 100LL at my airport is $6.29. You can find it around $6 but if you can't shop you can also pay closer to $7

[Sixracer]

I use the 87 non eth... for approx $3.50 a gal. The 100 LL is $6.39 (approx) at my home air port and $4.99 at another airport 25 miles away. I don't use it as a $$ savings. I am using it as a mixer to keep the Cont. from lead fouling the ex valves & plugs. I'm happy with the results after having sticking Ex valves on a fresh topend.

[GAHorn]

From Teledyne Continental (who, to my knowlege, makes no addt'l income from use of avgas...but might from use of mogas):
Automotive Gasoline in TCM Aircraft Engines
Teledyne Continental Motors would like to remind its customers that the use of automotive fuels in TCM aircraft
engines not only represents a potential safety of flight concern, but can also significantly affect cylinder life and
durability.
Engines produced by TCM are FAA certificated to a minimum grade of fuel conforming to ASTM D910-grade
100LL or 100 aviation gasoline. Early engine models such as the O-200A & B, O-300, and O-470 series are
certificated to grade 80 aviation gasoline, also conforming to ASTM D910. Detonation margins, compression
ratio, rated power, engine cooling, fuel schedules, ignition timing, and fuel system vapor handling are established
and FAA certificated based upon use of a fuel conforming to ASTM D910. The use of any fuel not conforming to
ASTM D910 may compromise safety and/or result in significant mechanical difficulties.
Automotive gasoline is manufactured to the industry specification ASTM D4814 which does not control or
establish limits for octane rating, major antiknock constituents, or energy density (lower heating value). In
addition, critical properties such as vapor pressure and level of contaminants are not tightly controlled as with
AVGAS. Vapor characteristics for auto gas are inferior to AVGAS and result in a tendency for auto gas to more
readily convert to vapor. In addition, the lower octane rating of auto fuel can lead to detonation and pre-ignition
which may damage the engine. Alcohol content of auto fuels may also result in damage to o-rings, seals, and
other elastomer components in the fuel system.
It is important to note that automotive fuels are not subject to the high level of quality control applied to AVGAS.
The allowable concentrations of additives, contaminants, and water in AVGAS are precisely controlled by ASTM
D910. Automotive fuels within the United States are changing rapidly to meet ever more demanding
environmental regulations.
Fuel producers have advised that auto gas will be subject to continuing changes in the future, with additive
formulas varying widely. Current Federal and State laws allow properties of automotive gasoline to vary
seasonally and geographically. Some states do not even require that automotive gasoline conform to the ASTM
D4814 industry standard.
Current aircraft engines feature valve gear components which are designed for compatibility with the leaded
ASTM D910 fuels. In such fuels, the lead acts as a lubricant, coating the contact areas between the valve, guide,
and seat. The use of unleaded auto fuels with engines designed for leaded fuels can result in excessive exhaust
valve seat wear due to the lack of lead. The result can be remarkable, with cylinder performance deteriorating to
unacceptable levels in under 10 hours.
Field experience has determined the use of unleaded automotive gasoline to be the cause of premature cylinder
replacement due primarily to rapid and severe valve seat recession. Therefore, if you choose to operate your
engine on automotive gasoline, valve seat and guide wear may occur at an accelerated rate. TCM strongly advises
against the use of such fuels for reliability and safety reasons. Because of this, engine or parts warranty will be
voided where such fuels are used.
TCM understands the high cost of flying and is committed to the relentless pursuit of product improvements
leading to improved cost effectiveness. Unleaded aviation gasoline and next generation cylinder components are
integral to our strategic plan for that future. In the interim, we ask you to consider the adage of “...penny wise...”
when considering the use of automotive fuels in your aircraft engine.

[canav8]

So what about TCP? Oh yea, never mind.

[GAHorn]

The quantity of lead in 100LL can be as much as two GRAMS of lead per gallon. That doesn't mean thats what it has, however.
Avgas contains bromides to help scavenge the lead, and if the combutions temps are kept up above approx 1000-degrees it will keep lead deposits to a minimum. TCP also requires high combustion temps to be effective.

Here is an interesting read on the matter: http://www.shell.com/global/products-se ... avgas.html

And, from BP (excerpted):
Manufacture
Gasoline is manufactured from crude oil using various refinery processes to improve the quality and volume of fuel produced. Typically, a refinery will have a number of processes to make components which are then "blended" to give a fuel of suitable quality for the market.
Mogas is manufactured using many different refinery components to meet the demands of high volume production. Components often include reformate and alkylate, high octane materials, cracked spirit - an olefinic material - possibly oxygenated materials such as ethers (e.g. methyl tertiary butyl ether), alcohols (e.g. ethanol) and a host of other possibilities. If some of these components were used for AVGAS there could be disastrous consequences as discussed below.
AVGAS can only be made from a limited set of components of the highest quality. The octane and volatility requirements generally limit the choice of alkylate, isomerate and possibly reformate. As a result, only a limited number of the world's refineries have the capability to manufacture AVGAS. No ethers or alcohols are allowed in the blend as these have a low energy content and would reduce the range of aircraft. This is also captured in a minimum energy specification for AVGAS - there is no such specification for Mogas. ...
Volatility
A gasoline engine requires a fuel which is sufficiently volatile to allow easy formation of the air and fuel vapor mixture required for combustion, while not being so volatile as to cause bubbles of vapor in the fuel lines ("vapor lock") resulting in fuel starvation. Specifications are set to control these properties based on the fuel's vapor pressure and distillation characteristics. These are different for Mogas and AVGAS.

Mogas volatility is set to meet the requirements of ground based vehicle operation for particular regions and seasonal conditions. AVGAS volatility must meet far more stringent criteria for aviation use as atmospheric pressure and temperature can change dramatically during normal operations. For example, fuel warmed to 70° F on an airfield can, in a matter of minutes, experience a pressure drop of 17% as an aircraft climbs to 5,000 feet. The fuel must not cause vapor lock. Similarly, an aircraft descending from 10,000 feet to sea level can experience an almost 36° F swing in temperature. The cold fuel must still be sufficiently volatile as atmospheric pressure increases.
To meet these demanding criteria, AVGAS distillation and vapor pressure are tightly controlled. The result is a fuel which can perform in many different and severe conditions from the equator to the arctic, from sea level to many thousands feet.

After manufacture, small amounts of approved ethers and alcohols may be added as fuel system anti-icing additives. However, this is strictly controlled to meet particular operational requirements. High concentration of alcohols can attack fuel system components and cause seal swelling/failure. They can entrain water into the fuel and promote phase separation into water + alcohol/fuel phases, which may cause engine failure. AVGAS specifications help protect the aviator from these hazards.
AVGAS, and other aviation fuels, are very carefully controlled at the refinery and in the distribution system to ensure no contamination by other products. Red, green and blue dye, respectively, are added to distinguish between AVGAS 80, 100 and 100LL for instance. Quality control follows every batch ensuring it is clean and on specification, ready for use. Overall, AVGAS is the highest quality gasoline a refinery can manufacture...

Many different specifications exist for Mogas across the globe to meet different climatic, environmental and economic requirements. Similarly to AVGAS, the specifications are agreed between the industry members. The aviation industry has no influence over these specifications, while the automotive industry has no influence over AVGAS specifications. ...
Detergent Additives and Gum
Detergent additives are now widely used in Mogas to improve engine cleanliness by reducing soot built-up on valves and injectors. These additives are not present in AVGAS because it contains additives which have been approved for aviation use and are listed in the specification.
Any new additive for AVGAS must be stringently tested to ensure a safe and satisfactory performance.
The detergent additives in Mogas have not been approved in aviation fuels/engines which operate under different conditions to ground based vehicles.
In addition, AVGAS must pass a severe storage stability test to ensure that prolonged airfield/aircraft storage does not result in excessive gum deposits which may block fuel lines and filters. High levels of gum are often linked to the detergent additives and cracked spirit used in Mogas....

[hilltop170]

George-
Your last two posts should be in a Avgas/Mogas topic thread of their own!

[blueldr]

That sure is one helluva lot of wordy CYA in blue type by Continental. How in hell do you suppose EAA or Peterson Aviation ever managed to get MOGAS approved?

[GAHorn]

That sure is one helluva lot of wordy CYA in blue type by Continental. How in hell do you suppose EAA or Peterson Aviation ever managed to get MOGAS approved?

They didn't get Mogas "approved". They got certain aircraft/engine combinations approved to run on Mogas of a particular specification (which is no longer available.)

Avgas is "approved"...for all airplanes.