What’s the best oil for my engine? Our oil expert weighs in on this reader’s question

I have a Lycoming AEIO-360 in my Pitts S1S. I have been running AeroShell 100W Plus for years. Some buddies I fly with have been using an Amsoil oil (I’m not sure the number). What is the best oil and weight to run in this engine?

Thanks.

CHUCK ROBERTS

via email

Chuck, yours is one of those questions that may have several answers, but I’ll take the easy way out and tell you what I’d do if this were my engine. First, if you’ve been using AeroShell 100 Plus for years and have had good service from it, why change now? I always feel it’s hard to argue with success, so if it was me, I’d stick with what you’ve been using.

Regarding the Amsoil that your buddies are using, I’ll say that I’m not aware of any Amsoil product currently on the market that meets the specification for oils approved for use in any Lycoming engines. If you’ll check Lycoming Service Instruction 1014M at your local maintenance facility, it will tell you the MIL Spec and SAE specifications that the oils must meet for use in Lycoming engines.

Again Chuck, my personal opinion would be to continue to use what you’ve been using. Let’s hope that my fellow contributing writer, Ben Visser, will come to my rescue and weigh in on this subject.

FROM BEN VISSER, GAN’s oils and lubricants expert: Amsoil did produce an aviation oil about 10 to 15 years ago. It was taken off the market because it did not absorb the lead by-products of combustion.

This resulted in a build-up of gray tacky deposits in the ring belt and prop that caused control and oil consumption problems.

The company does not have an approved product for a Lycoming engine. If your buddies are using Amsoil, they are either using some old product that did not work well or they are using an automotive product that also can cause problems.

I would say that you are using the best available product for your engine, so don’t change.

Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to: AskPaul@GeneralAviationNews.com.

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at Visser@GeneralAviationNews.com.

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