I did a little research on engine oils, here is what I’ve found, starting with a summary valid for our horizontally opposed six cylinder engine:
- Summary: our options appear to be:
- Aeroshell W100 and CamGuard
- Aeroshell 15W50 by itself (it already has additives for antiwear/corrosion)
- Aeroshell W100Plus by itself (already has additives for antiwear/corrosion)
- Phillips 66 X/C 20W50 and CamGuard
Based on this I recommend a single weight oil in summer, so W100 and CamGuard is a good option there. Full disclosure, I’m a CamGuard believer, I use it with every oil change on my 180 (whose engine is now 700+ hours over TBO btw).
I recommend a multi weight oil in winter unless we are very diligent about thoroughly preheating the engine. From the above, it appears we can use 15W50 by itself, or Phillips 66 X/C 20W50 and CamGuard. Personally I’d lean toward the latter, with our application.
I derive this summary from the information below, which came from two articles:
- https://www.boldmethod.com/blog/2013/11/aircraft-oil-mineral-ashless-dispersant-synthetic/
- https://www.aopa.org/news-and-media/all-news/2013/february/19/all-about-oils
- Oil types: Quoted from boldmethod.com: There are two main oil types used in aircraft engines: mineral oil and ashless dispersant (AD) oil. Both types are made of mineral oil – a refined, petroleum based oil. However, AD oils have added chemicals (additives), which collect debris inside the engine and carry them to the oil filter. Unlike mineral and AD oil, synthetic oil is not made from whole crude oil. There are some synthetic blend oils used in aircraft engines, but they aren’t as common. Shell Oil tested all-synthetic oils in aircraft engines, and what they found wasn’t good. At 600 to 900 hours, the engines began to burn more oil and lost compression. “When the engines were disassembled, we found that the piston rings were covered with a gray tacky substance that was primarily made up of the lead by-products of combustion.”
- Break in oil: also quoted from boldmethod: Many pilots have learned to use straight mineral oil while breaking in a new engine. It’s thought that mineral oil is less viscous (less slippery) than AD oil, and that it will allow the piston rings to wear in the cylinder walls more quickly. However, not all manufacturers recommend this practice. The Continental Motors engine break-in guide recommends straight mineral oil, while Lycoming recommends AD oil when breaking in all turbocharged engines. What should you use? Check your engine’s manual and follow the manufacturer’s instructions – always the best bet for long engine life.
- Oil selection: Quoted from AOPA: When selecting oil, the first thing to consider is viscosity. Simply put, “viscosity” is the measure of a fluid’s resistance to flow. Most air-cooled aircraft engines are designed for SAE 50-weight oil at operating temperature (approximately 210 degrees Fahrenheit).
In fairly stable, warm environments, a straight-weight oil such as Aeroshell 100, W100 or Phillips 100AW is a good option because these 100 oils all perform to the SAE 50 spec. In slightly cooler temperatures, straight-weight 80 oils will also work for some engines because they perform to SAE 40. If you have ever had to break in a new engine, you may have been told to use mineral oil. Mineral oil is a straight-weight oil that has no chemical additives and is typically used in engine and cylinder break-in to assist with the seating of rings.
For performance across a wider range of temperatures, it’s best to use multi-weight oil. Multi-weight oils are typically semi-synthetic, utilizing an added polymer to make the oil flow like a lower-viscosity oil in colder temperatures, yet still perform the same as a straight-weight SAE 50 oil at operating temperature. The most common multi-weight oils are AeroShell 15W50, Phillips 66 X/C 20W50, and Exxon Elite 20W50. The numbers in the name of the oil indicate the range of straight-weight oils that the multi-grade covers. For example, Phillips 66 X/C 20W50 oil has the viscosity of 20 weight oil in low temperatures for faster lubrication on cold starts and the viscosity of a 50 weight oil in high temperatures to protect the engine after it is fully warmed up. - Additives: again quoted from AOPA: The first and most important type of additives is ashless dispersants (AD). Ashless dispersant oils have an additive in them to aid in scavenging debris and carrying it to the filter or screen. This is a very important quality, given the relatively high wear of aircraft engines and the amount of combustion acids and other contaminants that get past the cylinder rings and valves.
Finally, the last category of additives is anti-wear and anti-corrosion additives. Oils such as Exxon Elite 20W50, Aeroshell 15W50, Aeroshell W100Plus, and Phillips 66 100AW include varying combinations of anti-wear and/or anti-corrosive additives. That said, products such as ASL CamGuard and AVblend can be added directly to non-additive oils such as Phillips 66 X/C 20W50. In these times when airplanes are flying less, I recommend using some sort of anti-corrosion additive in your oil. Please note that these are both FAA-approved additives. You should never use an unapproved additive, regardless of what you might hear around the hangar water-cooler.