What oil should you use?

Many pilots want to know what oil to use and where to get it.

To answer these questions accurately, I sent a questionnaire to the four main oil companies that supply lubricants to the general aviation industry. I received nice replies from Shell and Phillips, a note from BP that said the company was changing personnel and that they would get back to me, and an e-mail from Exxon that said that everything is on its website (ExxonMobil.com).

The first question I asked: What is your product line-up for piston-powered aircraft?This was a two-part question, asking them to identify mineral break-in oil qualified under Mil-L-6062/SAE 1966 and ashless dispersant (AD) oil qualified under Mil-L-22851/SAE-1899.

The line-up for straight mineral oils includes Shell’s Aeroshell oils and BP’s Castrol Aviator S oils in 65, 80, 100 and 120 grades. Phillips does not offer single grade mineral oils, but does offer a multi-grade mineral oil, Phillips 66 Type M 20W-50. Exxon Mobil does not offer a mineral oil.

As far as single grade AD oils, Shell offers Aeroshell Oil W oils in grades 65, 80, 100 and 120; BP offers Castrol Aviator A oils in grades 80, 100 and 120; and Phillips offers Phillips 66 type A oils in grades 100 and 120. Exxon does not offer a single grade AD oil.

Although there is no separate Mil spec, there is an additional classification for anti-wear oils that meet FAA Airworthiness Directive AD 80-04-03. Single grade oils that meet this spec are BP Castrol Aviator oil AD grades 65, 80, 100 and 120, Shell’s Aeroshell Oil W Plus in grades 80 and 100, and Phillips 66 Type A 100AW oil, in 100 grade.

What about multi-grade oils? Phillips offers 20W-50 and 25W-60 oils qualified against the Mil-L-22851/SAE-1899 spec. The 20W-50 is designed for opposed engines, while the 25W-60 is aimed at radial engines.

Shell offers a 15W-50 semi-synthetic oil that meets the Mil-L 22851/SAE-1899 spec and AD 80-04-03. Also meeting those requirements is Exxon’s semi-synthetic Elite 20W-50 oil.

Which brand and grade do you need for your particular engine? That’s a decision for each pilot. For example, when breaking in an engine, always check with the engine manufacturer and/or rebuilder for their recommendations. Lycoming recommends breaking in its naturally aspirated engines on mineral oil, but its turbo-charged engines on AD oil.

After break-in, Lycoming recommends using an oil that meets AD 80-04-03, while Continental does not specify either way.

My experience is that the anti-wear oils are beneficial for low-usage aircraft and mandatory on some Lycoming models.

Meanwhile, the debate between single grade and multi-grade will probably last forever.

In my experience, the multi-grade oils offer an advantage in cold weather starting because their improved flow characteristics ensure that oil gets to critical bearing surfaces quicker. In warm weather, I think that single grades offer an increased margin of protection in your engine. Plus, they leak less.
In my next column, I’ll delve into specialty oils and lubricants and who to call for availability and specific applications or problems.

For more information: AeroShell.com, Phillips66Aviation.com, AirBP.com and ExxonMobil.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 [email protected].