Plane & Pilot
Tuesday, August 9, 2011

Caring For Your Aircraft

Part IV: From selecting the correct grade to changing it at correct intervals, knowing your oil is important

Thus, multiviscosity oil extends the life of your engine by working well at different extremes. "A pilot should look at where he or she flies, and how often," says Royko. "That will point them to the proper multiviscosity oil if that's what's best for their operation."

Royko also recommends that pilots "spool down" their oil temperature after a long flight with a slow taxi, or by letting the engine idle for a bit before shutdown. "Racing to the hangar and shutting it down is not good for the engine. On warmup, bring the oil temp up gradually. Don't firewall the throttle a few minutes after starting either."

He says a careful oil analysis is valuable, or even cutting the oil filter yourself, removing the filter media and running a magnet through it to look for metal shavings, especially in the nooks and crannies, to check for possible issues.

There's so much more to oil than can be covered in an article. Lucky for pilots, AeroShell and others have several online resources that cover all kinds of valuable information. Whether choosing between single and multigrade oil, or discovering the best ways to handle oil changes and engine performance, there's a lot to learn. Shell has a complete knowledge center on the web at Phillips 66 also has an aviation resource center online at Both offer great information to help you keep the lifeblood flowing in your engine.

Important Oil Information

When learning about oil, it's valuable to know what the different terms mean, and what the facts are about different types. Since many myths abound, we talked to our experts and compiled some terms, facts and interesting information about your engine oil.

Mineral Oil—Non-synthetic oils come from earth-bound minerals and are said to be "mineral oils." The term describes a base-lubricating oil distilled from crude oil. In the aviation world, the term "mineral oil" refers to a pure (no-additive) oil often used to break in new or newly rebuilt piston engines. This type of oil helps "seat" the rings, valves and other components. Because it has no additives, it isn't designed to carry away contaminants.

Approved Oil—This refers to any brand name of oil that's produced under the specification SAE J1966 (for mineral oil), or SAE J1899 (ashless dispersant grades).

Ashless Dispersant—This used to be called "detergent" oil. It's an additive in aviation engine oil that prevents sludge and other harmful deposits by making them soluble and carrying them away. The contaminants end up in the oil filter or remain suspended in the oil until it's changed.

Multiviscosity—An engine oil that meets more than one SAE grade by passing tests at both high and low temperatures. These oils pump quicker at startup (compared to fixed-grade), flow faster to the upper valves and produce a thicker film at higher temperatures. The first number designates the viscosity at low temperature, and the second refers to its high-temperature viscosity.

Mixing Multigrade and Single-Grade Oils—While this used to be a bad thing, today's oil formulations allow mixing of multigrade and fixed-grade oils. So, a pilot may use something like a 15W-50 grade in the cold winter months, and then switch to a W100 in the summer without issue.

Drain Oil When It's Hot—Though this may be difficult in some airplanes, experts recommend you drain the oil only when it's hot. This avoids the settling of dirt and water on the parts of a cold engine, and more of the contaminants stay suspended in the hot oil, to be carried away from the oil pan.

Why Oil Turns Black—When straight mineral oil turns black, it's because it has oxidized and needs to be changed. Dispersant oil is designed to turn black as it carries away soot and other contaminants. Change oil based on engine time, not on color alone.

Synthetic Oil—Synthetic oil is formulated in a laboratory, not distilled from earthly components. In aviation, 100% synthetic oil hasn't caught on as much as in the automotive world, because it doesn't perform well with aviation fuel. The lead by-products of combustion in an aviation engine (because of the fuel) aren't compatible with synthetic oils. AeroShell has, however, developed a partially synthetic oil that performs well in aviation engines.


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