I saw this article today from Flying Magazine:

http://www.flyingmag.com/technique/tip-week/vent-engine?cmpid=enews041916&spPodID=030&spMailingID=25282648&spUserID=NDc4NjIyNzUxMwS2&spJobID=782952512&spReportId=NzgyOTUyNTEyS0

I have heard of people removing the oil cap post-flight but it never made much sense to me. While the engine is running there is air moving in and out the crankcase, so it is not like it is "trapped". And when parked the engine is free to vent out the breather tube. Wondering what your take is on this practice?

I had a rather "retentive" hangar mate once who capped his exhaust pipes and ran his breather tube to a small pump system to evacuate moisture.
Seemed overkill to me.
But, he was a Maule driver with a big Lyc. to worry about.
I just tried to fly the schmuck outa my 4-banger.

Author of the article needs to figure out if he is talking about oil TANK or what looks to be the crankcase. Early planes had separate oil TANK with "dry" crankcase.

Could be wrong again - still willin' to larn.

Zzz Can we get a litle yellow thingy for HYPERBOLE?

I've done it for years, at least when parked in a hangar.

Moisture is converted to vapor in the case. That heated vapor rises to the top of the engine case. Shut down the engine, and this moisture condenses, if trapped in the case. That moisture stays in your engine till you fire it up again.

Escape out the breather? Ever look at your breather? Usually, they exhaust out the BOTTOM of your cowl. So, you're thinking that warm, steamy air is going to DESCEND down through your breather while the plane is parked?

So, how much does this really help? Prolly not much, but it can't hurt, and any moisture you can get out of that precious engine is good riddance.

FWIW, which may not be much.

MTV

I agree with MTV, you never see vapor coming out of the breather after shutdown but if you pop your oil cap it comes billowing out. I regularly pop my cap after running, if I don't and pop the cap after its cooled there is moisture dripping from the cap. Even if it helps a little it's easy and worth the extra 30 seconds it takes.

I agree that it would let a small amount of vapor out, but it could just as easily come right back. Unless all inputs and outputs are sealed with a desiccant it would seem to me that in a few hours time there would be no difference between an engine that was "breathed" and one that was not. Both will have the same level of moisture as the ambient air.

And not saying it would hurt, but it could increase the chance of taking off without a screwed on oil cap if one did an inadequate preflight. Either way we are probably splitting hairs, but that's what the Internet is for.

Sent from my iPhone using Tapatalk

scottf wrote: Both will have the same level of moisture as the ambient air.

Not true, there is way more moisture inside an engine than there is in the ambient air. Remember that the byproduct of combustion is water, and a proportion of this water ends up in the internal spaces of the engine. When you shut down, as the engine cools, the very humid air inside cools also and the water it carries condenses on the interior engine parts.

The idea behind 'venting' your engine is that by applying positive air pressure you remove the high humidity from inside the engine (vent it to the atmosphere) and replace it with ambient (dryer) air. In some cases, the replacement air is even run through a dessicant to ensure it is very dry.

My opinion is that if you are flying very regularly this isn't necessary. But if you have your plane sitting for any amount of time, this will prevent rust from forming on the all important steel internals (ie: cylinders, camshaft, etc).

Chris

It sounds good in theory, but I'm skeptical that in practice that it makes much of a difference.

Flying your airplane regularly is going to do much more to prevent internal engine corrosion than anything else.

scottf wrote:And not saying it would hurt, but it could increase the chance of taking off without a screwed on oil cap if one did an inadequate preflight. Sent from my iPhone using Tapatalk

Well, if that's the case, you'll figure it out really fast. From then on, you'll verify oil quantity and security of filler cap prior to EVERY flight.

If you don't already.

Does this procedure make a big difference? Probably not. But, there is a LOT of moisture inside that engine after shut down, and any of that you can allow to escape is a good thing.

MTV

It would depend how dry the air is inside the engine, to begin with. It could be a really bad idea.

The engine case will draw in new cold air through the breather, as hot air flows out of the open filler cap. You have to think about that cold air that's being sucked in - what is coming in with it?

In a place where the ambient air is very humid, it would have to be a bad idea to leave the cap open. Especially if you've been flying up high in cold air for extended periods, where the air is very dry. In a desert or on a tundra - probably a very good idea...

Electrical power transformers are filled with hot oil and have to "breath" the open air all the time. The ambient air passes through a descant before it enters the transformer's oil breathers. Leaving them exposed to the open air is considered a very bad thing.

I just had to have my C-90 in my J3 with only 130 hours on it rebuilt due to corrosion.
It was my fault I admit due to lack of flying. It sat in a somewhat damp hanger in New England. I ran on Philips 66 with Cam Guard but it still wiped out two lifters. It would sit for 2-3 months at times due to my other flying obligation and bad weather when home.

I looked into the issue and decided to do something about it. After a bit of experimenting I came up with a dehydrating system that seems to work very well. It was a closed loop in that dry air was pumped into the breather line and extracted out the oil filler cap.

There are commercial units but were more costly than I thought justified and none were a closed loop. The idea of the closed loop is that the desiccant lasts much longer as it would if you were drawing in moist ambient air to dry all the time.

Installed was a accurate low humidity meter that measured the returning air to the unit. It usually read around 8-10% which is VERY low.

It took about 1 min to hook it up and would run over 2 months without needing the recharge the desiccant which is simply putting it in the oven for a couple of hours. It is blue in color when dry and starts to turn pink when filled with moisture.

It uses a small aquarium pump to circulate the air which has negligible current usage.

If you fly weekly its not needed but for those that fly as I did it worked out very well. It obviously does need electricity available to operate.


T

I looked into the issue and decided to do something about it. After a bit of experimenting I came up with a dehydrating system that seems to work very well. It was a closed loop in that dry air was pumped into the breather line and extracted out the oil filler cap.

That sounds like a good idea to me. Ethanol blended fuel would last longer in a storage tank,also, if a desiccant was used at the vent.

Didn't PCV systems mostly fix that in cars? It probably would not be too hard to do a system up for our motors.

I wouldn't have a problem doing it, but I really don't think it would make a huge difference in the dry climate my airplane lives in, and frankly, I never thought of doing it. When I go to OSH each summer, I do plug the exhaust pipes along with all the other covers and plugs and what-nots, but that's an entirely different and very much more humid climate.

I really think the best way of removing moisture from the engine is to fly the airplane for a long enough time each time that it thoroughly warms everything and evaporates any trapped moisture. The hardest thing on the engine would be to sit there with it idling for a few minutes, and then shut it down.

Cary

Live in Puget Sound area and went for an engine dehumidifier rig.

http://maulepilots.org/forums/viewtopic.php?t=3798

another version:

http://maulepilots.org/forums/viewtopic.php?t=3212