Crankcase air dryer

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8413
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Crankcase air dryer

Post by 8413 »

I'm the proud new owner of a 140A with a C90. I live in the Pacific Northwest where we have wet winters and can't always fly as often as we should for engine corrosion prevention. I have a question about using a crankcase air dryer. From what I understand you would plumb it so that the dry air goes into the oil filler funnel (tube) on the engine. The prior owner said he keeps the oil level at 4.25qts. When I peeked into the tube, I could see the oil part way up the tube. It seems to me that for the air dryer to work, you would have to have a cap with a perfect seal to the oil tube so that the air could push thru the oil to get into the engine? If the seal was not perfect, all you would be doing is drying the air in the tube because it wouldn't push down thru the oil into the engine and eventually out the breather. Anyone have experience with using an air dryer that can tell me if I'm even thinking about this correct?
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Re: Crankcase air dryer

Post by 8413 »

I got no reply. Are engine dryers not very common on small Continentals?
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Re: Crankcase air dryer

Post by cdoughty »

I'm interested too!!! Flying in NE in winter I never see 180 oil temp and always get water out the vent line overnight. I take the oil filler cap off after flying to let a little moisture out. If I don't there will be condensation there the next morning. But on the C-85 the oil level is above the bottom of the filler neck, so opening the filler doesn't really let you purge the crankcase. the problem it seems to me is that you have saturated air at 140F in the crankcase when you shut down and that will condense as it cools. I'd be happy to just exchange that hot wet air with ambient air. I have a couple ideas on my to-do list, but so far my approach is just to fly the next day so it doesn't sit long!!
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Re: Crankcase air dryer

Post by 8102 »

The Tanis Manual states that the Dehydrator will not work with small Continental motors, an excerpt is provided below:

• The dehydrator will generally not work with small bore Continentals. These engines include those in this series: A65, A85, A90,
C65, C85, C90, 0-200.

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Re: Crankcase air dryer

Post by 8413 »

Thanks Gregg.
I would think as long as a good seal is made to the oil filler tube, pressure would build until the air pushes thru the oil and into the engine. I don't want to be experimenting though. I was hoping this was already a tried and trued process and ready for the advice of owners doing it.
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Re: Crankcase air dryer

Post by 8102 »

I would tend to agree that given sufficient pressure the dry air would blow through. Problem is the small "aquarium" air pumps that are used in these dehydrators don't put out much pressure. You could do an experiment to see how much pressure it takes to actually blow past the oil in the filler tube then see how much pressure an aquarium pump actually puts out. I would think Tanis tried that but maybe not. You could also try a DIY dehydrator and size the pump appropriately.

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Re: Crankcase air dryer

Post by 8342 »

Have you considered raising the tail to see if the oil is blocking the filler tube in an aircraft level position?
If the oil quantity is low enough it may be open.
Just a wag.

It is not hard to make a tail jack to bring it up to level.

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Re: Crankcase air dryer

Post by 8413 »

I "think" the Tanis dryer uses a fan instead of a pump to move the air. That may be why they say it won't work with small Continentals. A fan would not put out much pressure at all.

If I do this, I will probably go with a DIY solution with an aquarium pump capable of pumping air thru the oil in the filler neck.
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Re: Crankcase air dryer

Post by a64pilot »

you can install a drier and you can plumb it in almost anywhere, the engine isn’t perfectly sealed and a slight amount of air will leak past rings etc and make its way out, one tiny leak is all that is required, a cheap aquarium pump can’t build enough pressure to hurt anything.

The top of the oil level does sit higher then the bottom of the oil tube, meaning the tube is under the level of the oil. The cap is sealed.
This is why if you check the oil level by drawing the stick out and looking it will read higher then if you repeat the check.

The reason is the trapped air in the fill tube when it cools will pull a slight vacuum and pull the oil level up, giving a false high reading

While it doesn’t hurt, a drier won’t really do any good on our small Conti’s, Lycomings lose a lot of cams and it’s hoped that a drier will help keep a Lycoming cam from getting any corrosion and make it last longer, but a Conti cam doesn’t have this problem.

About the only corrosion issue on infrequently flown little Conti’s is Cylinder wall rusting, enough cycles of light rust and cleaning it off when the engine is run accelerates cylinder wall wear and you eventually end up with polished bores.

If that’s a concern, fogging the cylinders and installing desiccant plugs is probably more effective.

The driers haven’t actually seemed to have helped the Lycomings either, but a worn cam or lifters results in a $50,000 overhaul, so there are special oil additives etc for Lycomings, even roller lifters that require a special engine case and now DLC (diamond like coating) lifters.

But back to our little motors, if your worried about moisture, apparently raising the temp even slightly greatly reduces relative humidity, a light bulb in a boats engine compt will keep the engine dry as a bone, and not much is more humid than a boat on the water in cold weather.

However heating the engine directly is apparently bad, leaving an engine pre heater on always can cause condensation inside of the engine, so you need to heat the air around the engine and not the engine directly, so a lower wattage drop light in the bottom of the cowl will keep that engine slightly warm and dry.
Even a 60W light bulb puts out more heat than we realize, remember your Sisters Easy Bake oven? So be careful how big a bulb you use. it doesn’t take much.

But as you know, the best medicine / preventative is flying regularly, of course not all of us can
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Re: Crankcase air dryer

Post by 8413 »

Thanks for that detailed reply a64pilot.

One thing I'm curious about...my understanding is that Lycomings have cam corrosion issues because the cam is at the top of the engine. Apparently the oil drips off the cam and it corrodes after the protective oil layer is gone. How is it that our Continental cam's don't have that problem? I understand our cams are at the bottom of the engine. But the Continental cam is not in an oil bath as far as I know? Both Lycoming and Continental cams would be exposed to the same crankcase air when not running and it seems our cams would drip the oil off and corrode too? I'm not "arguing with success" but rather just curious what I'm missing. Is it that the crank drips oil slowly onto the cam while it's sitting keeping it oiled longer?
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