Is it okay for plane to sit for a few weeks?

[ronrapp]

Is it bad for the engine? Depends on the surrounding circumstances, such as: is it hangared, or parked outside? Is it in a humid environment or a dry one? How often does it sit for 3 weeks straight? If it's an occasional thing, it's probably not the end of the world. The average privately owned light GA airplane flies something like 40-50 hours a year, so many of them do sit. But if it's sitting 3-4 weeks on a regular basis, I'd expect the possibility of some issues over the long term.

As others have said, if it's not going to fly, don't move the prop or ground run it, because you won't get it hot enough long enough to get rid of the moisture inside the engine.

[tracy]

I would think a fresh oil change and filter would drain a lot of moisture out of engine, then periodically ground run it for 20 seconds as not to get it hot, but lubricate the internals ,would be helpful keeping everything lubricated without any extra moisture forming. This is assuming it’s grounded for maintenance or prolonged weather, and your there to run it.

[pa38112]

The amount of water produced by ground running is astronomical - In the gallons range. However only a small portion of that makes it to the oil.
Water in the oil does not really hurt a sitting engine. The problem comes from the protective oil dripping off of the cam and cylinder walls exposing the bare metal to Humidity in the air. It takes several days for the bare metal to become exposed. You can extend that to weeks by using Aeroshell 20W/50 oil and by adding Camguard. This buys you a bit of a safety margin for letting the plane sit a little. – You never know when work/weather/maintenance issues/life will force your plane to sit for a while.
It is important to understand that the moisture we need to fear is the humidity in the air, not the water in the oil. That water tends to be entrapped in the oil.
The humidity inside the engine would be the same whether you have fresh oil, or 100% water in your sump. I know this is not actually true, but it is true from a practical standpoint. In my opinion the most important things you can do are:
1. Use Camguard
2. Remove the dipstick after running. (While an engine is cooling the
moisture in the sump is released into the air and will then condense in
the upper regions of the engine, like the cam)
3. Use an engine dehumidifier – requires significant work for a regular
flyer, so I don’t find them practical. If you know in advance that the
plane will sit, then they are wonderful.

[MacCool]

Originally Posted by pa38112

3. Use an engine dehumidifier – requires significant work for a regular
flyer, so I don’t find them practical. If you know in advance that the
plane will sit, then they are wonderful.

It literally takes me 30 seconds or less to connect my dehydrator to my airplane...as much time as it takes to open the oil door and stick a rubber stopper into the dipstick tube.

[rocketbob]

Originally Posted by ronrapp

Is it bad for the engine? Depends on the surrounding circumstances, such as: is it hangared, or parked outside? Is it in a humid environment or a dry one? How often does it sit for 3 weeks straight? If it's an occasional thing, it's probably not the end of the world. The average privately owned light GA airplane flies something like 40-50 hours a year, so many of them do sit. But if it's sitting 3-4 weeks on a regular basis, I'd expect the possibility of some issues over the long term.

As others have said, if it's not going to fly, don't move the prop or ground run it, because you won't get it hot enough long enough to get rid of the moisture inside the engine.

Just did an annual inspection on a pristine Piper Archer that's hangared in a well-insulated heated floor hanger that is temperature controlled year round. 22 hours on the airplane last year. Cylinders were full of rust. Its the acids and moisture in the oil that do harm. Not the environment.

[JonJay]

Originally Posted by rocketbob

Just did an annual inspection on a pristine Piper Archer that's hangared in a well-insulated heated floor hanger that is temperature controlled year round. 22 hours on the airplane last year. Cylinders were full of rust. Its the acids and moisture in the oil that do harm. Not the environment.

I read an article recently whereby they tested several dehumidifiers. They found all of them worked to lower humidity levels in the case. However, cylinder humidity remained unchanged. If you believe that article, dehumidifiers would do nothing to prevent cylinder corrosion.
I run Aeroshell 15/50 Semisynthetic in my airplanes. I believe a quantity oil with appropriate additives helps a great deal. Both of my airplanes have sat at one time or another for a few months for various reasons and I have never had any corrosion issues, at least in my cylinders.

[thinkn9a]

It says you can see rust as soon as 2 days,… but letter calls for maximum of 30 days (in reasonably dry environment) without taking further action


It calls for vapor phase corrosion inhibititor, etc. (called Vci in letter now called vcpi at spruce) If I know I will down for a while I put this in and fly before it sits for a while.

[PilotjohnS]

In the future, when we are all using unleaded avgas, is there a better engine oil one could use that would allow longer down time between flights?

[ronrapp]

Originally Posted by rocketbob

Just did an annual inspection on a pristine Piper Archer that's hangared in a well-insulated heated floor hanger that is temperature controlled year round. 22 hours on the airplane last year. Cylinders were full of rust. It's the acids and moisture in the oil that do harm. Not the environment.

If you say so. I'm just a pilot, and about as far from an A&P as one can get.

I sometimes wonder if hours flown, by itself, always tell the whole story. Would flying 30 minutes every weekend have the same result as flying 22 hours the first month and then sitting for 11 continuous months?

Do airplane engines that live in Arizona suffer the same corrosion as those that live in coastal Florida, given the same amount and frequency of use?

[von_flyer]

I think engine dehydration is a valuable tool in preventing engine damage from moisture during sit times and even short term down time. Using a temperature and humidity data logger I documented the effect of dehydration on a Lycoming O-360. While this is relative to crankcase environment only, cylinder dehydration is a more difficult problem to solve. My data can be found here. I use dehydration between all flights not just for long term storage. EAA recently had a Webinar talking about dehydration that had some interesting information on the topic and can be found here.