Piston engines have specialized requirements when it comes to oil changes. Piston engine oil changes come with dedicated tooling and procedures, and they are useful to monitor the engine health. In this feature, we shall review the peculiarities of this important task, best practices, and factors related to oil consumption.
Important Task
An aircraft piston engine oil change is a maintenance operation that can be performed and planned by the owner either every 25 hours or every 50 hours depending upon the respective engine recommendations, explains Bill Ross, vice president of product support at Superior Air Parts. "In order to perform the oil change, there is a wealth of different tools and requirements that are needed. The tools that are used include safety wires, a calibrated torque wrench, a socket for the oil filter," he says. "Those doing the change will also need a clean container to catch the oil. This is very important, because they should not use a dirty container but need something very clean to drain the oil into in the event that they have an abnormal oil filtering."
Changing the oil is so important because it is an indicator of internal engine health; it is especially important to change the filter and to look at it, explains Ross. "We do this to remove contaminants that build up within the oil, we also do it to replace the oil additive package that is put in by the oil manufacturers, i.e., the emulsifiers and chemicals that are in the oil to prevent rust and to carry particles in suspension," he says.
Task Interval
As regards oil change intervals, each aircraft owner should consult the respective engine manufacturer’s recommendations, recommends Ross. "In the maintenance manual, there should be a recommended interval and approved oil for the specific engine. Oil change intervals may be based on what the aircraft is used for. As an example, an aircraft involved in agricultural applications, where it is operated in dusty conditions, would require changing the oil more frequently than an aircraft that is operated off paved runway and only for pleasure flights," he affirms. "Those intervals and recommendations can be found within those respected engine maintenance manuals, and they can also be found in other service documents, such as service bulletins."
Ross believes that there is a risk of skipping piston engine oil changes or doing them improperly to the point of forgetting to replace the oil before running the engine. "Very often people skip changing piston engine oil or do it improperly and, based on our experience, using a checklist in concert with the respective engine maintenance manual is the best defense against the risk of starting the engine without any oil in it," he says.
Best Practices
There are some best practices as to how one should properly perform piston engine oil changes. "Owners who have never changed the aircraft engine oil before should consult an aircraft mechanic to teach them how to properly perform the oil change, it may take a couple of times before the owner feels comfortable in carrying out the operation correctly," says Ross.
To properly change piston engine oil, it is important to focus on what type of oil to choose, not mixing oil and water, understanding if there is excess oil, properly inspecting a filter, and analyzing oil consistency and additives, according to Ross. "We should not take for granted the information we learn about the health of our aircraft piston engine through a proper oil change. The trick here is really understanding what is 'normal' and what is 'abnormal'. Additionally, oil is the lifeblood of our engines, and selecting the right grade and type is critically important," he says.
Oil Consumption Rates
Another important thing to do is to continuously monitor oil consumption rates, as a change in consumption can indicate a problem, explains Ross. "I keep a small log of oil usage in my personal aircraft so I can track when oil was added and the time intervals between those additions," he affirms. "This type of detailed information can be very helpful to the maintenance provider when it comes time for an annual inspection or when diagnosing engine problems."
Oil consumption lubricates the cylinder parts and ensures good cooling of the piston and piston rings, affirms Ross. "To calculate the maximum brake-specific oil consumption there is a formula found in engine operations manuals. The number is based on percentage of power and, in most cases, is closer to one-quarter of an hour. The engine manufacturer must demonstrate that the engine/airframe combination will run out of fuel before running out of oil," he says. "During the certification phase, manufacturers must demonstrate that with the sump full and the engine consuming the maximum amount of oil at idle, there is no danger of the oil leaking out of the engine before the fuel."
Engines come in many different designs, and each consumes oil at different rates, based on age, use, percentage of horsepower
