Why No Avgas?

   ~This article may be the most important section of this blog in that it deals with a widespread issue that UL Power, as of this writing, still has not resolved and only recently has decided to make note of in their manual.
   Back when I bought my 390is, a rep from UL Power made it known that these engines really weren't designed for the use of leaded fuels, and that some guys were trying additives like TCP to help reduce the build up of lead deposits. He even went as far to say that a top end overhaul may be needed in as little as 200hrs if running 100LL exclusively.  At the time I just assumed that the additives would solve the problem so I started using a safer alternative to TCP called Decalin. My engines performance was slowly deteriorating due to blow-by, as mentioned in another article, but at the same time, something even worse was happening inside the combustion chambers. When my heads were removed for the cylinder honing, I noticed thick excessive layers of carbon and lead deposits caked onto the piston heads and valves. I planned on getting a 3 angle valve job in order to improve air flow and gain a little performance, so I was going to let the machine shop clean it all up. The machine shop called me after removing the valves and wanted me to come in and see what they had found. Every single one of the exhaust valves had been eroded like they were sand blasted at the 45 degree angle. All new valves would need to be ordered. All I could think about was what I had been told years ago by the UL rep. Investigating this further, I found that several others have had valve issues and coincidently the ones running 100LL as a primary fuel source. Obviously, the Decalin wasn't doing its job and there have been no reports that TCP has been a help either. Recently I was told by Ray Lawrence, of UL Power, that he himself won't use straight 100LL due to the issues he's been seeing in other customer engines as well. He has reassured me, however, that those using at least a 50/50 mix of Avgas and auto fuel (Mogas) are running without problems so far. Right then I decided to take his advise and no longer run 100LL exclusively.
   As you can imagine, this puts a major damper on cross country flying as 93 octane auto fuel is almost non-existent at airports around the country. On top of that, auto fuel has been a major problem in composite fuel tanks and have even caused fatalities within the canard community. Needless to say, I purposely built my long ez for the use of Mogas and boy am I glad I did! I now run a 50/50 mix of 100LL and pump gas and have not had any issues so far. Also, a recent borescope shows a much cleaner combustion chamber since switching to the mix, but i've also been adding marvel mystery oil to my fuel and keeping the CHT's up.
   Over in Europe, Mogas is the standard and 100LL is harder to come by. Apparently the Belgians aren't motivated to design their engines around the use of 100LL much like Rotax won't. Advertising that 100LL can be used, knowing it's damaging affects, doesn't sit well with me. For us flyers here in America, we just have to hold out for the arrival of a 100LL alternative fuel to hit the tarmac. Until then, Stay away from 100LL if you can, and if you must use it, make sure to dilute it with auto fuel as much as possible.

Damage from 100LL

Large carbon and lead deposits from exhaust manifold

Excessive deposit buildup

Excessive deposit buildup

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