By: Ted March
E-mail Address: tedmarch@worldnet.att.net

I'm wondering if any other aircraft owners have had experience with AeroShell 15-50 semi-synthetic oil. This is a half-and-half mix of mineral and synthetic oil. Shell says it has the advantages of both without the well-know disadvantages of a straight synthetic, like the infamous Mobil1. They say the AD mineral oil component of AeroShell cleans and holds in suspension deposits. While the synthetic component offers superior lubrication for startups because it clings to parts better and during hard running because it is tougher than mineral oil.

I have used synthetics for years in my cars and am sold on them. So recently I put AeroShell 15-50 in my Cherokee 140. I could tell it was easier starting on cold winter mornings. And it didn't seem to drain down as much during week-long idle periods. And my oil consumption went down measurably. I was happy with it. Then one day just as I was on a takeoff roll, the plugs on one cylinder fouled and I had to abort the flight. Not a great time to have a cylinder crap out. Before this, I had a normal runup and everything seemed to be fine. It happened fast. I have been flying this plane for six months nearly every weekend without a fouling problem. I am very conscious of proper leaning enroute and I do a lean burn during shutdown.

Now, a couple weeks after switching to AeroShell I suddenly have bad plug fouling problems. Is it possible that AeroShell has more tendency to get in the combustion chamber? I know from experience that synthetics are more slippery and seep through small spaces easier. Whether car or plane engine, you can see the difference in leakiness on the outside of the engine. So now I am wondering about this oil.

Any opinions on this?

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