understanding semi-synthetic formulation: Aeroshell W 15W-50

understanding viscosity grade of mineral single grade oil.
  1. Understanding viscosity grade of mineral single grade oil
  2. Understanding semi-synthetic formulation in multigrade Aero
  3. Understanding the additives in AeroShell Oil W 15W-50 formulation
  4. Benefits of using AeroShell Oil W 15W-50
  5. Oil changeover
  6. Exceptions to the use of AeroShell Oil W 15W-50
  7. Summary Table

AeroShell single grade oils are available in different viscosity grades. The following table provides approximate guidance for using AeroShell Oil based on the average ambient outside air temperature at engine start-up.

AeroShell SAE Grade 40, 50 and 60 oils are mineral single grade oil (both the ashless dispersant ‘W’ oils and the W Plus oils). The viscosity index of these mineral oils is fairly uniform due to the nature of the base oils used.

This means that whilst higher grade oils such as AeroShell Oil W 100 and AeroShell Oil W 100 Plus oil may be satisfactory for operation during warm weather, it may well become too thick to pump effectively at the lower temperatures experienced at start up. Conversely, if lower grade oils such as AeroShell Oil W 80 and AeroShell Oil W 80 Plus oil are used during hot weather, it may not prove to be viscous enough to support the loads required when at elevated operating temperatures.

This is the reason many engine manufacturers advise that the oil grade is changed as climatic temperatures change. You should always refer to your engine manufacturer’s recommendations for clarification on which grade to use at which temperature.

  1. understanding semi-synthetic formulation in multigrade AeroShell Oil W 15W-50.

[The chart shows the typical temperature to viscosity of AeroShell W Oils, source: Shell Aviation SAV-SIL-202101]

The concept of multigrade oil is to have an oil which can be used in all temperature (i.e. it’s viscosity changes less with temperature). In this way in cold weather it will pump effectively, but still support high load at high temperature. And in warm weather, it supports high load without a compromise by having reduced viscosity. The ideal solution to this is to use an oil which has a higher viscosity index.

Semi-synthetic oils use a blend of mineral oil and synthetic hydrocarbon oil. Due to the naturally high viscosity index of synthetic oil – its viscosity changes less with temperature as compared to mineral oils.

Another advantage of using a semi-synthetic oil is that the synthetic component of the oil has a higher thermal stability and therefore degrades at a slower rate than mineral oils. This leads to the oil both performing as an effective lubricant for longer, and also producing less acidic compounds, the by-products of oil degradation.


understanding the additives in AeroShell Oil W 15W-50 formulation.

Anti-Wear Additives

A load carrying anti-wear additive is blended into AeroShell Oil W 15W-50 and AeroShell Oil W 80/100 Plus. The additive does not react until it is needed. The way this works is that if two moving parts start to make contact, then friction causes heat to be produced – this heat causes the additive to alter its chemical structure and it then reacts with the metal surfaces, coating them with a protective layer. If the two moving parts then try to make contact again, then they are separated by a layer of the additive even if no oil is present. In this way the additive is only deposited where it is needed. This is particularly useful in limiting wear when lubrication is marginal, such as on engine start up and on components which experience unusually high load – typically cams and cam followers. This has also been recognised by Lycoming and the additive is classified under the name LW16702, and is mandated for use in some of their engines. Therefore, using AeroShell Oil W 15W-50 means that no additional additive needs to be used if you operate one of these engines.

Metal Passivators

“Metal passivator” additive is added and reacts with the surface of copper components found in piston engine, forming a protective layer which separates them from the oil, thus preventing the copper from degrading the oil.

Corrosion Inhibitors

One more additive used in AeroShell Oil W 15W-50 and AeroShell Oil W 80/100 Plus is a corrosion inhibitor. This inhibits the formation of rust in the engine – a common root cause of engines not reaching TBO (Time Between Overhaul). Rust is often found in engines as used oil is acidic and, combined with dissolved water from the atmosphere, causes corrosion.

your benefits of using AeroShell Oil W 15W-50.

  • Year-Round Product Solution

    • Multi-grade Technology (The 25 Second Advantage) – Protects critical engine parts on start-up by reaching full pressure in the front gallery more than 25 seconds faster than competitive oils
  • Plus Technology Additive Package

    • Corrosion protection which is particularly useful in engines which are not highly utilized
    • Contains Lycoming approved LW16702 anti scuffing additive that provides superior protection against wear
  • Semi-Synthetic Blend

    • High viscosity index allows use in any season or geography year round
    • The synthetic portion of the oil does not degrade as quickly as mineral base oil, is able to withstand higher temperature, and improves the viscosity index of the oil


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Source of publication: Shell Aviation SAV-SIL-202101 

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