Paul...and anyone else who wants to read it. TCP is called out to help the spark plugs in the big aircooled engines. It however does a lot more. In overhauls of engines that ran a steady diet of leaded fuels for all their lifetime i can attest to the effectiveness in all areas of the engine. For example in checking the inside of the camshaft, hollow and nothing going on inside, we see with no TCP paste build-up in that is has to be dug out like silly putty stuck in the rug. In engines with TCP that is a much lighter slurry that washes out with little fuss. The same is seen in old gally bores and other areas that most will never see except at overhaul time in a shop. The overload clutches, old versions before the lead slinger holes were added, lead would build up to the point that the clutch breakaway level was double a new version. Essentially turning the clutch into a 3 lb brick spinning on the shaft. Not much use when locked up with lead. The TCP will keep them relatively clear and the sludge is easy to clean up at inspection times. The same issue for the sprag clutch on the starting side. Without TCP we had extensive issues with lead and resulting sprag failure. The use of TCP and the newer parts significantly reduced sprag failure to a point where it is almost a none issue.
One very special note on liquid cooled heads. if you run the coolant nearer the hotter side, up where you would see oil temperatures, then lead formations are not much of a problem. On the injected engines we run a much leaner burn that really helps with that. This will greatly reduce lead buildup in the head and valve area itself. Lead is mostly a problem in the carb version engines in that they tend to run rich especially when people overuse carb heat systems or run them rich. Rich conditions promote excessive lead buildup and should be avoided. If you have a carb engine with carb heat, and that is always a good idea, use if sparingly and when necessary. Some experimental builders have excessive engine bay heat by design. This is nice in that there is very little chance of carb ice but it creates a very rich mixture that is a problem with leaded fuel contamination.
I agree with what you have observed with MOGAS. In general as long as the water is kept in suspension in the fuel corrosion is not a problem. Most issues are from extremely long storage issues where phase separations occurs from saturation of the fuel with water. In the old days of certified aircraft we were all told to fuel the aircraft directly after flight. The metal tanks then had only a small space for condensation to accumulate. With AVGAS given there is nothing to absorb water from condensation it will drop right away to the bottom of the tank. Always sump the fuel before flight, especially important with AVGAS . Todays LSA type aircraft see a lot of variables in fuel tanks. if you have metal tanks the condensation issues are still there. The differences are in what fuel you might be using. MOGAS, even even in the european standards have alcohols that absorb water to some extent. In the USA ethanol is blended into some 90% of the normal automotive fuel supply.
European EN228 * For gasoline with max. 3.7 m% of oxygen, allowed oxygenate contents are methanol 3 v%, ethanol 10 v%, iso-propanol 12 v%, iso-butanol 15 v%, tert-butanol 15 v%, ethers with five or more carbon atoms 22 v%, and other oxygenates 15 v%. For gasoline with max. 2.7 m% of oxygen, allowed oxygenate contents are methanol 3 v% and ethanol 5 v%.
On a side note. When Rotax was asked to allow the use of ethanol in their aircraft engines it was done after a lot of consideration. The test engine in the field was an aircraft in Brazil that ran some 25% ethanol all its operational life in a flight school. The engine was some 8 years old and was overhauled and the components analyzed by representatives from Rotax at the time. The results were that it was pretty normal. The issue however is they could not allow 25% as the emissions from that level of ethanol are very bad for the environment. Benefits from high levels of ethanol emission wise do not begin until over 30% by volume. NOx emissions and other emissions were a major concern. The engine in question, a carburator 912ULS, has no way to allow for changes in the fuel density and ratio of the burn. The timing is fixed and we can't use a knock sensor or full electronic, auto adjusting, system to compensate for the different fuel mix. This is also true of the iS, it is a Map system, it is not auto sensing in that it does not change timing on its own. That all said the safe bet was that 10% would be a safe compromise to allow. The issue is then up to the OEM, builder, to be sure that the fuel system is suitable. (fuel tank, lines, filters, etc) to use ethanol.
Anyway...i like TCP if you have to use lead. Decalin has a milder carrier for the TCP and you can take it with you in the aircraft if you travel to treat fuel as you need it. The Alcor TCP fuel treatment has very specific instructions to not take it in the aircraft with you due to the volatile solvents to carry the TCP in suspension. (unless it is in your fuel) Just keep that in mind.
Cheers
