A chill is in the air: What does that mean for owners?

Ben Visser


Each fall I get asked the same question: What should I do to my aircraft before I put it away for the winter?

The questions usually come from people with open cockpit planes or people who plan to spend the winter away from their aircraft. The answer depends on how long you will be storing your aircraft, and what the climate conditions are.

Let us assume that you live in the Midwest, with moderate humidity and normal freezing temperatures in the winter, and that the aircraft will be stored for approximately six months. The first step is to change the oil and filter (if so equipped) before parking your plane. Most pilots like to change oil before they start flying in the spring so they leave the old oil in over the winter. This is a very bad practice because you will have all of the acid, moisture and other contaminates in the oil during the long storage period. This promotes rust and corrosion, so change it before storing it and then just go flying in the spring.

Make sure that you fly your aircraft and get the engine up to normal operating temperatures before changing oil. Then drain the oil hot. This may not be the easiest way but it does ensure that the oil has most of the contaminates in suspension.

After you change the oil, run it up to ensure that fresh oil is on all of the engine parts. Now put your plane in the hangar.

Many pilots will plug the intake and exhaust to reduce the amount of moisture and contaminates that will be drawn into the cylinder. Remember that when your engine is sitting idle, at least one intake and exhaust valve will be open. As the temperature goes up and down, moisture is drawn into the cylinder and will condense onto the surface of the cylinder. This can lead to surface rusting and eventual pitting of the cylinder wall.

Always check your manuals for additional steps recommended by manufacturers.

If you are going to store your plane for longer than six months, you may wish to take additional steps. Some people will back out the valve adjustment so that all of the valves are closed or they will spray the cylinder walls with oil. Both of these will help, but you need to remember and readjust the valves before flying. If you fog the cylinders, I recommend that you remove the lower plug and crank the engine over before starting. You do not want to hydralock a cylinder as that can be detrimental to engine parts. Desiccant plugs are also helpful.

On extended storage, I have heard of pilots filling the crankcase completely full of oil. This works but can be messy and is dangerous if you forget to drain the crankcase and cylinders before flying.

The fuel system should be OK for six months. Remember, auto fuels should be used within six months of purchase. If you are going to store your plane for a significantly longer period, I would recommend that you switch back to avgas for a few tankfuls prior to storing. Avgas is usually good for a year or so.

The climate is important because of temperature and humidity. If you live in the desert southwest, the amount of rusting activity will be so low that you could store an aircraft for well over six months with just normal precautions. Similarly, if you live in a very cold climate, the amount of total moisture in the air is very low, so rusting activity should be very low. Conversely, if you live in the Gulf Coast area, you will probably have high humidity and temperatures, plus significant temperature variation. This will lead to higher rusting activity. Here you may wish to shorten your storage period or increase the precautions.

Aircraft engines were built to be flown regularly. They are a bit like food you can freeze it if you use some precautions, but eventually it can become freezer burnt.

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at Visser@GeneralAviationNews.com.

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