- For aircraft that operate in temperate climates year-around, we recommend using Aeroshell W100 monograde oil with one pint of ASL CamGuard added at each oil change.
- For aircraft subject to un-preheated cold starts where multigrade oil is preferred, we recommend using Phillips X/C 20W-50 with one pint of ASL CamGuard added at each oil change.
- We recommend taking an oil sample at each oil change and having it analyzed by Blackstone Laboratories in Ft. Wayne, Indiana.
Decades of field experience has shown clearly that monograde (single weight) oil is superior at preventing corrosion compared to multigrade oil. Unless multigrade oil is required because the engine will be subject to un-preheated cold starts (never a good idea), we suggest using monograde oil.
The only oils that we actively discourage our clients who use leaded avgas (100LL) are synthetic or semi-synthetic oils. In our experience, Aeroshell 15W-50 semi-synthetic is particularly problematic; the issues include:
- Lead sludge buildup, especially in ring grooves and crankshaft bore
- Corrosion issues
- High copper readings in oil analysis.due to triphenyl phosphate attack on copper components
- Aggravation of TCM starter adapter slippage due to synthetic content
- Aggravation of oil leaks.
Many of these problems result from the synthetic oil that makes up 50% of Aeroshell 15W-50’s base stock. Synthetic oil works fine in automotive engines that have very low blow-by and operate on unleaded fuel. For piston aircraft engines that run on highly leaded fuel and have lots of blow-by, the use of synthetic oil can be problematic.
Years ago, Mobil sold a 100% synthetic aircraft oil called Mobil AV 1. It was pulled off the market after Mobil was sued by thousands of aircraft owners whose engines were ruined by lead sludge buildup. It turns out that synthetic simply cannot hold lead salts from 100L in suspension, so they precipitate out in the form of nasty sludge that can cause serious problems with the engine, propeller and prop governor. As a result of this, there are no longer any 100% synthetic oils on the market for piston aircraft engines.
Aeroshell 15W-50 is 50% synthetic. Exxon Elite 20W-50 is was 25% synthetic, but has been discontinued. Phillips 20W-50 is 0% synthetic (and 100% mineral oil), which we think is the best choice if you need multigrade oil (because you will be doing cold starts in sub-freezing temperatures without a pre-heat).
W100 is much, much more viscous at room temperature, and so it doesn’t strip off critical engine components as quickly during periods of disuse. If you don’t require the cold-starting properties of Phillips 20W-50, we suggest you use W100 for improved corrosion prevention.
In addition to using single-weight oil, airplanes that live in very high corrosion environments should have a good anti-corrosion additive package added to the oil. We believe that the best available corrosion inhibitor is ASL CamGuard. Optimum corrosion control can be achieved by using Aeroshell W100 with one pint of ASL CamGuard added at each oil change.
Alternatively, Aeroshell offers an oil called W100 Plus, which is W100 with a corrosion inhibitor package added. We think CamGuard does a far better job, but W100 Plus is okay if you prefer to use it. However, W100 Plus contains tricresyl phosphate anti-wear additive, which can sometimes attack copper parts and cause high copper readings in oil analysis. This is one reason that we prefer W100 non-Plus with CamGuard added.
Note that many Service Centers do not stock CamGuard, and a few are reluctant to use aftermarket additives. Savvy clients who find themselves in this situation are encouraged to purchase CamGuard on their own and add it themselves after taking delivery from the Service Center after each oil change. You can order CamGuard online at:
For an airplane exposed to the worst of both worlds—sub-freezing cold starts and high corrosion—we recommend using Phillips 20W-50 plus one pint of CamGuard.
We hope this helps clarify the reasons behind Savvy’s oil recommendations. As you’ve already discovered, this is a controversial subject on which you will find a wide variety of divergent opinions. Now you know ours, and the carefully studied rationale behind them.
We also recommend starting the use of or switching to Blackstone laboratories for oil samples. They do a much better job than other labs in our experience, and have the newest state-of-the-art equipment. Free oil sample kits may be ordered online at:
Make sure the oil sample results are emailed back to you (not the Service Center), and post the Blackstone report to the Savvy ticket system when you get it. We suggest you fill out the oil analysis submission form yourself to ensure that the data is accurate.