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HomeBuyer's GuidesTime to change your oil?

Time to change your oil?

Time to change your oil?
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Time to change your oil?Time to change your oil?Time to change your oil?Time to change your oil?Time to change your oil?Time to change your oil?Time to change your oil?

Changing the oil in a general aviation piston aircraft is a fairly simple process and certainly something that an aircraft owner can do but there is a definite sequence of steps that must take place in order to do the job properly.

The Basics

While changing the oil might appear to be as simple as opening the oil drain valve and disposing of the used oil, closing the drain valve, replacing the oil just drained away with “fresh” oil, and making a log entry, this task can be much more challenging.  As an aircraft owner performing “maintenance”, you will be held to the same standard as any maintenance person in that, by regulation, you must have the appropriate technical data available, and the tools necessary to the perform the job. When the oil change is complete a log book entry must be made stating what was done, the date, the tach time, and your signature, as well as your pilot’s license number. When you sign the log book, you are attesting that the work you have done is satisfactory for flight.


When in contact with the skin for prolonged periods used motor oil is known to cause cancer among laboratory animals and it is safe to assume that repeated contact with used motor oil may be harmful to humans as well. For this reason it is advisable to use gloves when handling used motor oil containers, oil filters etc., and to dispose of used motor oil properly. Wash your hands after contacting used motor oil (especially before you eat). Contaminated clothing can also be a problem; a pair of inexpensive coveralls can come in handy. You may want to invest in a pair of safety goggles for eye protection since, in addition to handling motor oil, there is safety wire that must also be handled (and cut) while changing the oil. 

When and Why Does Oil Need to be Changed?

The reason for changing the oil is to remove contaminates which have accumulated since the last oil change and are suspended in the oil since the last oil change. Operating with excessive amounts of contaminates can cause unnecessary engine wear. Oil change intervals can be up to 50 hours (with oil filter) but should be no more than 4 month intervals as recommended by engine manufacturers. In order to most effectively remove contaminates, the oil in the engine must be circulated and warmed to normal operating temperature before it is drained. It is very important to drain all of the used oil so you are not mixing contaminated with “fresh" oil.

The oil filter must also be replaced during the oil change process because as much as a quart of potentially contaminated oil can be left inside the engine in the old filter element. Some aircraft require that the oil cooler line also be drained, along with the oil in the sump, and the oil filter. Other aircraft have a screen in place of an oil filter; this must be opened, the cavity drained and the oil screen checked for foreign material (such as metal flakes), cleaned and re-installed using a new gasket. When adding oil, always make certain that not only is the container you are using completely clean of foreign matter, but that the funnel (or other filling device you may be using) is also spotlessly clean. Always wipe the oil filler cap area and dipstick clean before removing so as to prevent dust or dirt from entering the engine. It makes no sense to change the oil, then add contaminates along with “fresh" oil.

Where to Change the Oil?

Some airports have areas designated specifically for the purpose of draining oil, or for performing other “minor maintenance" activities. Additionally, most airports or FBO's have containers for the proper disposal of used oil. A major environmental concern is the contamination of sewers or storm drain systems by used motor oil. Should this happen you could be in for a fine or worse. Changing oil can be messy and it doesn't take much oil on the hanger floor or tarmac to create a big mess. A drip pan, large piece of cardboard, or a bag of clay, "kitty litter" which will absorb spilled or dropped oil can be very handy to have around should the need arise.

What Type of Oil and How Much to Use?

Refer to the owner's manual for the engine, or the aircrafts pilot's handbook. The engine owner's manual contains a wealth of information and is a great publication to have as a reference; it will list the types of approved oils as well as the grade of oil approved for your engine. Generally, multi-viscosity ashless dispersant oil is preferred since this type of oil has been proven to reduce wear while keeping contaminates in suspension. Always check with your mechanic regarding engines that have had a recent top overhaul or complete overhaul. This is because some engines require break-in oil of a specific type for up to the first 50 hours of operation.

What Do I Need to Do the Job?

(Note that items listed in BOLD may be required depending on the application and the configuration of your engine.)

It goes without saying that the aviation oil of the quantity and grade approved will be required. You will need a drain oil bucket with enough capacity (at least 2 gallons and ideally 5 gallons to handle the total oil sump quantity that can be expected. You will need a hose of some type to transfer the sump oil (used oil) into the collection bucket. Most aircraft have “quick" (spring loaded) oil drain valves, but a few have the standard oil drain plug which must be safety wired in the “closed" or plugged position. The safety wire on the plug will have to be cut, and the drain plug unscrewed. Most modern aircraft engines will have an oil filter; a few aircraft will have a screen which will require a new gasket.

You will need a replacement oil filter of the specific “approved" type, some .032 diameter safety wire, and some Dow Corning DC 4lubricating paste for use on the rubber gasket on the oil filter. Dow Corning DC4 comes in a small tube which will be enough material to last 20 years! For the thrifty pilots out there, you may want to share some of this material along with your buddies to help defray some of the cost. An oil filter wrench can generally be used to remove the oil filter, but you will have to experiment with several types and sizes to determine which one works best for your application. Since the installation specifications for the oil filter require a torque value, you must use a torque wrench to properly “seat" the oil filter. There is a fixture on the rear of the oil filter for the purpose of applying the proper amount of torque to the filter during the installation process and lugs for safety wiring. This fixture is NOT to be used to remove the filter.

After installing the oil filter it is necessary to safety wire (.032 diameter) the filter so that it cannot “back off" from the installed position. A very light coating of DC 4 paste on the rubber oil filter seal (just enough to make it look “wet") will prevent the seal from “welding" itself to the engine, which would make it nearly impossible to remove. If you should encounter a stuck oil filter, a substantial strap wrench such as is commonly used in the plumbing trade, comes in handy during difficult filter removal situations. Clean any oil residue from the outer surface of the filter, and use the strap around the metal base of the filter, (not the sheet metal housing) as the housing may collapse before the filter itself moves. You can even get creative and use some sand paper between the strap and the filter to help with the grip of the strap wrench. If you cannot get the filter off don't risk damaging the engine. You may need the help of a professional.

Used oil filters should be cut open at each oil change with an oil filter cutter and the pleats inside the filter inspected for metal filings. Oil filter cutters can be very basic or somewhat elaborate, but any tool designed for the job will work. A basic lever type can opener can even work if you are careful not to introduce the metal shavings this may produce into the filter media. Be careful not to cut yourself on the sharp edges of sheet metal.

To complete the job some basic hand tools will be required (Keep in mind that cheap tools are no bargain as you risk damaging the aircraft or engine. Poorly designed tools may even lead to personal injury). When dealing with safety wire, arm your tool belt with a good pair of safety wire pliers; wire cutter pliers, duck bill pliers, and needle nose pliers may prove useful as well. A good pair of lock wire pliers can in most cases be used in place of the other 3 pliers I listed but it is good to have all types on hand just in case you need them. In addition, you will most likely need a set of end wrenches to open up a drain plug or remove a cap off an oil line to the oil cooler. A torque wrench with an appropriate socket will help in “seating" the oil filter in place. Both straight blade and Phillips # 2 screwdrivers may be required for removing cowling fasteners. Several rags or a roll of paper towels will be required for clean up as well as some type of hand cleaner/ soap and water.

Completing the job

After draining the oil and replacing the oil filter or screen, it is best to check that all the old oil has been drained from the sump and the sump drain valve, plug etc is installed and safety wired (if necessary) before adding new oil. When adding oil it is important to note that although the capacity of an oil sump can be 8 quarts, it is a generally accepted practice to add less than the “full" amount of oil such as 6 to 7 quarts. Check with your mechanic to see just what he or she recommends. After adding the oil, make sure that the dip stick agrees with the amount of oil added. The oil level as measured on the dip stick should be a “ball park" confirmation of the oil added. Fresh oil is sometimes difficult to read but given the correct lighting you will be able to see it.

Before you close the cowling, make certain that excess oil (from spills, etc) is cleaned up so that you do not confuse an existing spill or leak with a new one. Verify that the oil cap, dip stick, quick drain or drain plug is installed, safety wired if required, and no evidence of any leakage. Most importantly, check for any tools that may have been left in the engine compartment or around the aircraft, and promptly remove them. Be sure you account for all tools and material brought to the job: are they in the tool box or where they are supposed to be? After ensuring that everything is OK, it is safe to close the cowling and position the aircraft in order to perform a run up and leak check.

After engine start up, check that the engine has oil pressure and that pressure develops within the specified amount of time. Generally no more than 20 to 30 seconds of engine run at idle power after start up is allowable; refer to your engine's operating manuals for specifics. If you have no indication of oil pressure within the time allowed, shut down and do some investigation before starting the engine again.

Log Book Entry

After the engine run up and leak check is completed, physically check for oil leaks by opening the cowling and looking under the aircraft for puddles of oil on the ground. Make one final check of the oil level indicated on the dip stick. Complete the job with a simple entry in the engine log book. Date, tach or Hobbs time, description of the work preformed, your signature and your pilots' license number are all that is required.

Final Thoughts

Changing the oil can be simple and rewarding. It gives you an opportunity to be personally involved with the maintenance of your aircraft. And doing so allows you take pride in a job well done. Looking beyond the oil change, those concerned about the long term health of their engine might consider setting up an oil analysis program, which can detect abnormal trends during the operating life of an engine. If you go this route, be sure to follow the directions exactly when you collect an oil sample. There are some companies that will analyze both the oil filter and the used oil and give you a full report. This service makes sense, as sometimes significant metal can be found trapped in the oil filter media, yet only a small amount may be left in suspension with the oil sample.

After you have changed the oil a few times you will know what you need to do and how to do it. You may have even developed a few skills that you didn't know you had! It does take some practice to make a safety wiring job look professional but practice, as the saying goes, makes “perfect". When doing preventative maintenance, keep an eye out for anything unusual and investigate with your mechanic before your next flight. Remember that minor aircraft maintenance issues which are let go can become quite costly to repair.

Enjoy the time with your plane, and learn as much as you can- knowledge is power!

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