The Air Affair -> Features -> Change Your Aircraft's Engine Oil

The Grob Chronicles

Change Your Aircraft's Engine Oil

by Ross Oliver
October 6, 2006

Changing the engine oil and filter is one of the preventative maintenance items that pilot owners are permitted by the FAA to perform. Aircraft owners can save a few dollars and gain more experience with their aircraft from a perspective other than the pilot seat.

We pilots have checklists for many phases of flight operations. I find that checklists are equally important for maintenance operations. I have owned my Grob 115C for nearly 5 years, and perform my own oil changes. This article presents the checklist and "amplified procedures" I have developed to help my oil change operations run smoothly and efficiently. Since these procedures are specific to my aircraft, you may need to make adjustments to suit your own aircraft.

NOTE: Consult a qualified aircraft mechanic before attempting for the first time.

Most of the tools required for an aircraft oil change will already be found in most home workshops. The only aircraft-specific items are the safety wire pliers, safety wire, and oil filter cutter.

Tools

Supplies

The wet wipes are handy for cleaning up small oil drips and runs. The alcohol will disolve the oil, where a rag or paper towel would just smear it around.

I always fly the aircraft immediately prior to changing the oil. This drives out any accumulated moisture in the oil for a more accuate oil analysis, stirs up any sludge and sediment in the oil sump for more complete removal, and makes the old oil flow easier. Since I will be working in close proximity to the propeller, I take the opportunity before shutting down to verify the correct operation of the magneto ground.

Having the aircraft roll away during maintenance can ruin your whole day, so make sure it is not going to wander off.

Adjust as necessary for your own aircraft.

The oil can drain quickly when warm, so be ready to take the sample before you start draining.

My Grob's Lycoming O-320 has an oil quick drain installed in the sump, which is very handy. The drain, however, is right next to the exaust heat exchanger for the carb heat. A Scotch Brite pad placed against the heat exchanger makes a great insulator to prevent burning the back of my hand while opening the quick drain.

Since I have to work out in the open, I need some way to prevent wind from blowing away my the empty collection jugs. So I place them in a the cardboard carton containing the new quarts of oil. The weight of the oil containers holds the carton in place and stabilizes the collection jugs while the old oil is draining.

Allowing some oil to drain before taking the oil sample assures that the sample will not be contaminated with any debris or old oil left in the hose, or dregs from the bottom of the oil sump.

Remove the drain hose from the jug and fill the oil sample container. With some practice, you will be able to fill, but not overfill, the 2-ounce sample container and return the hose to the jug without spilling (still hot!) oil on your hand, down the outside of the jug, or all over the tarmac (or hangar floor, for you lucky aviators who get to work inside).

Use a permanent marker to mark the new filter with the date, aircraft registration number, and engine time. Apply a thin coating of Dow #4 dielectric compound to the oil filter gasket. This will help prevent sticking or damage when the filter is removed. If Dow #4 is not available, new engine oil can be used.

This is also a good time to inspect the rest of the engine and accessories. I check the brake fluid level, look for any oil leaks, damage to the spark plug wires, missing or broken fasteners, condition of the engine baffling. Clean up any leaks and note their locations so they can be checked again in the post-oil-change leak check.

After all the oil has drained, close the quick drain and allow a few minutes for any remaining oil to drain from the tube. Remove the drain tube from the quick drain, and wipe the quick drain clean.

Because you can never get all the oil out of the drain tube, I store it with the ends together side by side, wrapping a paper towel around the end to collect any remaining oil and securing with some scrap safety wire.

This prevents them from being stepped on or knocked over.

Now comes the potentially messiest part of the operation. My oil filter mounts horizontally, and therefore retains almost half a quart of used oil. After only a turn or two of the filter, this oil will do its best to spill out onto the engine, nose gear, lower cowling, and tarmac/floor. Such a mess is incredibly difficult to clean up because the oil gets into all sorts of inaccessible nooks and crannies, only to drip out or be blown out later on.

I have tried several methods of coralling this oil. The method that seems to work best for me is to wrap a plastic garbage bag around the underside of the filter, and securing it to the engine mount and firewall with clothes pins. This leaves both hands free to unscrew the old filter and install the new one.

Use the side cutters and needle nose to remove the safety wire from the filter. Some people cut only the engine side, and leave the wire attached to the filter. I prefer to remove the wire entirely to avoid having a sharp wire flopping around while unspinning the filter. To loosen the filter, I use a rubber strap wrench. This can be a little hard, as the filter is smooth and sometimes slippery. Channel lock pliers also works well.

Oil will continue to drip out of the engine when the filter is removed, so have the new filter ready for immediate installation.

After installing the new oil filter, remove the plastic bag and any collected oil, taking care not to snag or tear the bag. Use the funnel to drain the collected oil into one of the waste jugs.

Place the old oil filter open end down in the funnel to drain into one of the waste oil jugs.

Hand tighten the oil filter until the gasket makes contact. Then torque to the manufacturer's recommended value. The Grob's engine installation does not allow enough room to fit a torque wrench onto the end of the oil filter, so I use the old standby method of tightening 1/2 turn after gasket contact.

Applying safety wire to the filter, while not difficult, does take practice. It is not unsual for me to need 3 or 4 attempts to get satisfactory results. DO NOT be tempted to re-use safety wire. Bending and twisting work-hardens the wire, making it too brittle to unbend and use again. Always start over with fresh wire. Not only is this required practice, you will get better results with fresh wire as well.

The main variables are what length of wire to start with, and where to clamp the safety wire pliers to get the twists to end in just the right spot to attach to the filter. Once I get the wire tight on the filter, I usually twist the final "pigtail" by hand.

Wipe the drain clean so you can check for leaks later.

The oil capacity of my Grob's O-320 is 8 quarts. However, I have found that anything over 7 quarts is quickly sprayed all over the belly of the aircraft while in flight. Minimum quantity is 6 quarts. So I pour in 7 new quarts. The new oil filter will retain about 1/2 quart, leaving an after-change level of 6.5 quarts.

If I have my usual spare quart of oil in the baggage compartment, I will use it as part of the fill-up, and one of the newly-purchased quarts becomes the new spare.

After installing fresh oil and replacing the dipstick, it is time for leak check. Before starting the engine, it is worthwile to perform one final set of checks: oil drain closed, oil filter secure, oil sump contains the proper level of oil. Wipe clean around the oil filter and drain to ensure any leaks will be easier to identify.

Start the engine, and verify proper oil pressure. Run the engine for 2-3 minutes at approx 1000 RPM. Shut down and check for any oil leaks, paying particular attention to the areas of the oil filter and drain. Re-check the dipstick for proper oil level. The level will be slightly lower because the new oil filter will retain some of the oil.

Check the engine compartment for any tools, rags, safety wire scraps, or anything else that doesn't belong before closing up the cowling.

As long as you're alread dirty, this is a good time for other preventative maintenance tasks:

Wait! You're not done yet!

The final step in the oil change is to cut open the old oil filter to inspect for any metal particles that may indicate excessive engine wear or impending failure. I put this step last because I usually do it back in my garage after returning from the airport.

You may want to use disposable gloves for the next step. Aside from being generally messy, waste oil from aircraft engines that burn 100LL does contains lead, which is toxic.

Clamp the old filter in a vice, open end up. Use the filter cutter to cut through the outer casing just below the filter base. There is a spring inside the filter, so be careful the filter lid doesn't pop up in your face when the cutter breaks through the case.

Remove the filter element from the case. Use the hacksaw to cut the filter paper away from each of the metal ends. Then use a utility knife to cut the filter away from the metal plate. Once released from its metal frame, the accordian-folded filter paper is over six feet long.

Starting at one end, use a strong light to examine each fold of the paper for any collected material. Flakes of carbon are normal. These flakes can be distinguished from metal flakes by the fact that the carbon is not magnetic, and can be crushed between fingernails. Use a magnet to look for any metal flakes stuck in the paper. When passing a magnet beneath the paper, metal particles will move or "wave", whereas carbon flakes will not respond to the magnet. Don't hesitate to have an A&P examine any material you find.

Used engine oil is classified as hazardous waste in most areas, so be sure to dispose of the used oil and filter remains in accordance with local regulations.

The oil sample kit contains a postage-paid mailer for mailing the sample. Fill out the accompanying form (I also keep a copy for my records) and include with the sample. Results usually arrive in about a week.

Yes, pilot owners can make log book entires. Since an oil change is considered maintenance, the aircraft is not legally airworthy until the logbook entry has been made. I copied the text from a mechanic's earlier entry:

[Date and engine tach time] Serviced engine with AeroShell 100 Plus oil. Replaced filter. Ran engine to check for leaks. Opened and inspected oil filter for debris, none found. Sent oil sample for analysis.

Include your printed name, pilot certificate number, and signature.

If everything goes smoothly and I don't make any big messes, I can complete the oil change in about 1 hour. I figure I save about $80 to $100 by doing the work myself. Enough for one of those hundred dollar hamburgers!