Saturday, September 01, 2007

How to Change the Oil in a Mooney

Changing the oil is not the most exciting of topics to write about; however, I've learned a few tricks over the years that may help someone...

Mooney's designed their cowls to be tight. There is basically no way to change the oil without completely removing the top and the bottom cowl clam shells. It takes about 30-45 minutes to remove the cowl from a Mooney! This is a pain, so when I do it...I do everything I can while I'm in there.

Changing the Oil
The first step is fairly drain the oil. 36G has a quick drain plug, which makes oil draining a snap. You simply hook up a hose to the connector and open it. A trick to this is to run the engine before draining the oil. I typically fly the plane somewhere and then I drain the oil when I get back. The oil will drain much faster if it is warm. Another trick is to let it drain overnight. The more old oil that drains out of the engine the better. Don't rush this step. Let it drain completely.

After the oil is drained, the next step is to cut the safety wire and then remove the filter. Care must be taken when removing the filter. They are made out of thin metal. I highly recommend using the proper tools to remove the filter. You do not want to crush it by turning it by hand or a standard wrench. They can be nearly impossible to get off if they start to tare. It will also make a huge mess.

I have two different types of filter wrenches. The one above can be turned by hand and attached to a socket set. It works well for most conditions. I also have a special filter ratchet wrench for difficult ones. These tools are available just about anywhere that sells aviation parts.

Removing the filter always makes a huge mess. You need to be prepared for this so oil doesn't soak your tire. I wedge some old towels over the tire and other things I don't want oil soaked, then hold a bucket under the filter when I start removing it. Another trick I've used in the past is to use a old milk jug. You can cut the bottom out of it and leave the cap on. A milk jug is easy to cut and can be trimmed to fit around the filter catching the oil as it spills out. The filter can spin off and drop right into the jug. Take it to your drain bucket and open the cap. The oil will drain out without a drop getting on the floor.

After the oil is drained and the old filter is removed, the next step is to install the new filter and safety wire it. Care must be taken to safety wire this properly. You do not want it to spin off in flight. The safety wire should be pulling toward the tightening direction. So if the filter tries to spin off, the safety wire will stop it. A leak at the filter can quickly dump your oil overboard. Do not forget this step!

The final step in the safety process is to turn the end of the wire toward the can. It is very easy to cut your hands on safety wire, but if you turn the sharp edge in this will not happen.

The next step in the process is to make sure your oil drain is closed and to start filling the sump. A old mechanic trick is to pile all of the oil you intend on using on top of the engine. It is very easy to get diverted and forget how many cans of oil have been put into the sump. The oil filter, hoses and other components hold oil after the engine is run, so the dipstick is not reliable at this point. It will actually read higher until you run the engine (e.g. stick will indicate 7 quarts when it's actually 6).

After the oil is installed, the final step is to run-up the engine and then carefully inspect it for leaks. You will likely smell some burning oil when the engine gets hot. This is normal. Residual oil gets on the exhaust and other areas, but it will burn off in a few minutes. This step, again, is very critical. Oil changes seem simple, but people make mistakes. You need to check, and recheck to make sure that you are not leaking oil before returning the airplane to service. An engine can seize in a matter of minutes if a material leak develops.

Oil Analysis
Changing the oil is a good insurance policy. Aircraft oil is designed to hold and carry contaminants in suspension. The more particles the oil holds, however, the more abrasive the oil becomes. Dirt, Rust, water, etc. in the oil will slowly sand the inner parts of the engine and can also block oil coolers and other key components.

I highly recommend sending an oil sample at least once per year to a lab for processing. Labs use advanced equipment to detect very fine debris in the oil and identify them. For example, a high silica level would indicate that dirt is getting past your air filter. High iron, indicates that the metal parts in the engine have been sitting around without oil on them and rusting.

There are several labs that do this type of work. I have recently been using Blackstone Labs in Fort Wayne IN. They were a top pick by Aviation Consumer, so I thought I'd give them a try. What I like about Blackstone is they not only send you a report, but they write a personal note describing their findings. They will tell you if the iron or other components are high and what component in the engine is likely generating it. They will also show your engine sample and compare it to other like engines. I like this because I can see how I'm doing. Are we better or worse than other TSIO-36o's? Blackstone will let you know.

Open the Oil Filter
Lab analysis is very important, but equally important is opening up the oil filter and see what it has caught. An oil analysis will not tell you that a gear tooth chipped and fell into the engine, but the oil filter will probably catch it.

Opening a filter is a bit easier said than done. You can't just cut it with a hacksaw. You will generate metal from the filter itself, thereby contaminating your sample.

The first thing you need is an oil filter cutter. there are several on the market, but they are expensive. I like the AirWolf Filter Cutter pictured above. It isn't cheap, but it is high-quality and works well.

The oil filter cutter works about the same way as a plumbers pipe cutter. You slowly turn the filter cutter around the filter and then turn a blade knife a bit at a time. This causes pressure on the filter outer hull and will make a clean cut.

After the filter is apart, you want to first visually inspect the filter for large objects. Then you need to run a magnet around the filter and in the oil that spilled out looking for metal. You may find some hard pieces in the oil that are normal carbon buildup, but you should not find any metal. Metal large enough to be caught in the filter means something major is coming apart in the engine. Do not ever fly a plane if you find metal in the filter!

No comments: