How to select the right grade of piston engine oil
You need to choose the right grade of piston engine oil to maximise your engine’s performance and its life. Choose AeroShell Oils for running-in your engine and the AeroShell W range or W Plus Oils during normal operation.
There are four grades of AeroShell Oils and AeroShell W Oils to choose from, which differ based on viscosity. Engine manufacturer Lycoming advises which oil to use based on the average ambient outside air temperature at engine start-up:
- Below -12°C – Choose AeroShell Oil 65 with the corresponding SAE grade 30.
- -17°C to 21°C – Choose AeroShell Oil 80, W80, or W80 Plus with the corresponding SAE grade 40.
- 16°C to 32°C – Choose AeroShell Oil 100, W100, or W100 Plus with the corresponding SAE grade 50.
- Above 26°C – Choose AeroShell Oil 120, or W120 with the corresponding SAE grade 60.
However, this advice doesn’t apply to AeroShell Oil W 15W-50.
For large engines, the operator’s preference and experience often decides which grades to use. Generally, this depends on the climate in which the engines are operating:
- AeroShell Oil W100 or W100 Plus tends to be used in temperate regions.
- AeroShell Oil W120 is often chosen in warmer climates.
While most of our advice fits with many piston engine oils, there are special considerations if you have a radial piston engine or a vintage engine. You also need to consider when to change your piston engine oil, how to store it, and how to test it. Learn about each below.
When should I change piston engine oil after break-in?
Some aircraft manufacturers suggest straight mineral oil should be used to break in new or recently overhauled engines for the first 25 to 50 hours, or up to 100 hours, of operation. Or until the oil consumption is stable. After that, switch to ashless dispersant oil – the AeroShell W range.
Yet, some rebuilders and manufacturers, such as for engines like the Lycoming O-320H and O/LO360E, say you can use either straight mineral oil or ashless dispersant oil for break-in. For all turbocharged Lycoming engines, ashless dispersant oils are recommended from the start.
Check with your engine manufacturer or rebuilder to find out what oil you should use. To find out about when to change you piston engine oil during day-to-day operations, read the AeroShell Book.
How to store piston engine oil
You can store AeroShell W Oils for a long time without compromising on quality, properties, or performance as long as you’ve stored and handled them correctly.
How to use piston engine oil in radial engines
Thanks to their unusual parts, radial engines can run into problems not seen in other piston engines, so you need to choose a dedicated piston engine oil that can handle the heavy-duty stress. The right AeroShell piston engine oil to choose depends on the kind of aircraft, application, and the climate it’s operating in.
For ordinary operations, choose AeroShell Oil W120 in moderate or temperate climates and AeroShell Oil W100 in cooler climates. When breaking your engine in, choose AeroShell Oil 120 and 100 respectively. If AeroShell Oil W 15W-50 is approved for your radial engine, then you can use this too. All these oils are a reliable choice because they don’t contain zinc additives, which can destroy your engine’s master rod and bearing.
If you’re using your radial engine for agricultural operations then be mindful that it faces specific issues to do with dirt and overspray getting into the oil. To avoid this, keep your engine well-maintained, follow good flying procedures, and change your oil frequently.
How to use piston engine oil in vintage aircraft
A lot of the oils originally approved for vintage piston engine oils are no longer available. Check with the engine rebuilder or oil supplier what new oil to use if it was approved on aviation oil other than a MIL-L-6082 or a MIL-L-22851.
Don’t assume you can simply replace your old oil with new piston engine oils.
How to test piston engine oil
Make sure you perform oil tests periodically to give you chance to spot changes, rather than only noticing problems when it’s too late. Here’s how to test your piston engine oil:
- Regularly take samples – Take a sample midway through draining hot oil from the sump, as this’ll give you the best representation of how clean the oil is rather than if you sample from the top or bottom. Be sure to take the sample in the same way each time you test your oil, as inconsistency can lead you to mistakenly believe you have engine problems.
- Use a series of consistent tests over time – A series of tests will reveal changes and trends over time. Don’t rely on absolute values.
- Take samples in the same way – Make sure you take each sample the same way and at the same time interval. Always properly label them.
It’s all part of good maintenance to routinely check your piston engine oil so you can find problems before they can become major failures. Good maintenance generally involves spectrometric wear metal check and testing oil viscosity and acidity, which are services Shell companies can offer.
Bear in mind that there might be higher wear metal levels during break-in or after certain maintenance procedures.