O.K
I have found some, but not all of the information that I was after. The following is a copy of an article from the Textron Lycoming ‘Key Reprints’1996 edition. If any of you have this publication the article is printed on page 15.
I think that this article is very convincing, of course, everyone can make his/her own decisions. The question is; If you are intelligently reasoned by your engine manufacturer not to do something then, why to do it? Just for the savings of few pennies? I know what my decision will be.
The article’s tittle is:
Do Not Use Automotive Gasoline in Textron Lycoming Aircraft Engines That are Certified for Aviation Gasoline.
Automotive Gasoline Could Be Dangerous To Your Health – Reviewed June 1995
In Lycoming Flyer No.25 dated February 1976, we told operators not to use automotive gasoline in our aircraft engines and listed 7 reasons against its use. Service letter No. L199, dated January 1983, reiterated that policy by stating” Textron Lycoming does not approve the use of any fuel other than those specified in our latest edition of Service Instruction No. 1070. Although STC now make the use of automotive fuel, which meets minimum specified standards, legal for use in some aircraft, reciprocating engine manufacturers and most major oil companies do not approve. While it is true that octane levels appear adequate, these organisations are of the opinion that the varying Quality Control standard applicable to automobile gasoline produce undue risk when it is used in aircraft.
Several specific reasons are given for the non approval of automobile fuel.
1. Its use reduce safety. Although an operator may find that the engine runs well on a specific grade of auto fuel there is no assurance that fuel from the same tank will be of the same quality when purchased the next time. Risk is increased.
2. Its use void warranty, or result in cancellation of the owner’s insurance.
3. The storage characteristics of auto fuel are less desirable in comparison with the good storage characteristics of aviation gasoline. After several months, stored automotive fuel may suffer loss of octane rating, and tends to deteriorate into hard starting, along with forming gum deposits that cause sticking exhaust and intake valves, and fuel metering problems, resulting in rough running engines. The turnover of auto fuel is so fast that long lasting storage characteristics are not required.
4. The additives in automotive fuels are chemically different from those designed for aviation and contain auxiliary scavengers which are very corrosive, and under continued use can lead to exhaust valve failure. They also cause rust and corrosion in the internal parts of the engine. The allowable additives for aviation gasoline are rigidly tested and controlled. There is no uniform control of additives in automotive gasoline. Many different additives are used, depending on the fuel manufacturer. For example, one fuel company adds a detergent to clean carburettors. This additive creates a significant increase in the affinity of the gasoline for water which can cause fuel filter icing problems if outside temp. are cold enough.
5. The auto fuels have higher vapour pressure than aviation fuel. This can lead to vapour lock during flight because the fuel advise that auto fuels can have double the vapour lock pressure of aviation gasoline, depending on the seasons of the year, and the location because of climatic conditions. In addition, auto fuel also increases the possibility of vapour lock on the ground with a warm engine on a hot day.
6. Although fuel octane numbers shown on the pump of automotive and aircraft gasolins may be similar, the actual octane ratings are not the comparable due to the different methods used to rate the two types of fuels. Furthermore, aviation gasolines have lean and rich rating, i.e.100/130, whereas motor gas is not tested for a rich rating.
7. Automotive fuel used in an aircraft engine may lead to destructive detonation or preignition and potential engine failure at high power conditions.
8. The actual Mo-Gas fuel requirements range from meeting ASTM or government specifications only in 6 states, to few or no minimum requirements in the remaining 44 states, as opposed to the uniform strict requirements for aviation fuel.
SUMMARY:
Auto fuel is now being used as a substitute for Grade 80 aviation gasoline under STC’s issued by the FAA. Most major oil companies and engine manufacturers continue to recommend that aircraft piston engines be operated only on aviation fuel. Deterioration of engine and fuel system parts have been reported in aircraft using auto fuel in aircraft. Remember – pilot can’t pull over to the side of the road when fuel creates a problem with the engine.