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Leaving the oil filler cap ?Open? to vent moisture ? (For a bit)

laserman

Active Member
So I can’t find any thoughts on an open oil filler cap to let engine moisture escape from a hot engine ??

So after a nice one hour plus flight today , after a fresh oil change, on a 300 hour well maintained engine (oil temp running at 185F). I pulled the aircraft is back in hanger .. I pulled the dip stick and again saw the milky white oily mixture on the filler cap / filler neck (clearly water in the oil) and watch the vapors pour out..

I’m sure it was a mixture of mostly water and maybe some hydrocarbons.. I then watched as the water continued to condense on a good sized and cold (35F) chunk of aluminum I held over the open oil filler neck. I mean a ¼- ½ teaspoon over a 10-15 minute period. (yes engine breather tube clear)


With the oil filler cap left on.. There is no way that ½ teaspoon of water is ever going to get out of the engine .. A 2’ long 3/8ID crankcase vent tube.. that’s open ONLY BELOW the engine.. sure is not going to let the moisture escape..

It really made it clear why these aircraft engines rust for the inside out.. A sealed up engine has no chance for a reasonable life unless its flown A LOT.

So can it be as simple as leaving the oil filler cap off for a few hours... to a day.. Letting the moisture “Vent out of the TOP of the engine... ? Enhancing the moisture dissipation by leaving the engine heater on for a few hours ( Cylinder & oil pan heaters) Yes.. There is no way you would want to leave an engine heater on with a “Sealed-Up” engine.. The moisture just able to circulate inside the crank case. Rust.. Rust ..Rust...

So there is a nice $49 monitor module (amazon) that will record temp/humidly every minute for up to 20 days and then be downloadable to a smart phone or Excel .. With a slight mod.. and remote wiring of the sensor, so I can have the sensor in the crankcase after a flight.. I’m going to get some real data on this idea ..

Anyone else looked into the simple moisture venting concept?

Experiment #1

Nice flight.. Let cool over night ..

Next day.. Measure internal engine humidity for several days


Experiment #2

Nice flight.. Leave oil cap off.. With engine heat for 6 Hours.. Heat off.. Cap off..

Next day(1) .. Replace oil cap.

Next day(2) ..Measure internal engine humidity for several days


Give me a 2 weeks and I will have some real data

AL
 
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The problem I have always had with this is that I cant stand around long enough to fully vent it, and if I leave the dip-stick open I forget to come back later and close it...
 
I vent after ever flight. Probably get most of the steam to escape in first 10-15 minutes while I am wiping down the plane and filling out logbook. Put stick back in before I leave as don’t want critters to crawl down the dip stick.
 
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If you fly frequently, like 4 times a week, you probably won?t have to worry about it. But - I?ve never considered this ?venting? procedure and will be checking it out. In the colder months when I can?t fly as often, it seems like a sensible thing to do....
 
I fully agree with the above post. There's just too much risk in forgetting. With my dehumidifier I never remove the dipstick unless I'm immediately ready to install the dehumidifier bung and vice versa.
Regarding the humidity measurements, the way I have my unit set up is that the air exiting the crankcase goes into a jar which has a household, AAA battery powered humidity sensor. After shutdown my humidity sensor typically reads 70-80%, then drops down to 10-15% after a few hours of pumping dry air in from the dessicant.
http://www.vansairforce.com/community/showthread.php?t=157922
Once things get to about 30-35% (takes about 40 engine starts to achieve this) I put the dessicant in a baking tray in the oven for about 105?C and it's good as new.
Tom.
 
Experiment 3 ??

Forced air vent through breather tube during initial cooling phase.. with fish tank pump, or ballon inflator or other simple pump
 
SOP for me and would leave oil sump and cylinder heat on continuously.
No chance of forgetting the cap off if you check your oil before every flight.
 
I?ve been doing this as well. I am highly interested in your results, so please share your data. Thanks!
 
Back in the day, pulling the oil dipstick up and hooking it on the oil filler door was SOP for an A36 partnership we were in. Pretty much all the members did it, and it was darned obvious having the door propped open like that by the dipstick...missing that...well you shouldn't be flying if you didn't see it.

I was always amazed at the amount of steam rising out of the filler neck after a flight.
 
My SOP after the last flight of the day is to loosen dip stick Immediately after shutdown. It stays open until the next flying day. Visible mist comes out for first few minutes. Aircraft is hangared. SOP is to visually check fluids (oil and fuel) prior to EVERY leg. I learned this from an old timer (not a bold timer) with a lifetime of experience. It makes sense to me.

Bevan
 
Same

Yep open it up and prop the oil door open.
Ton of steam exits that has no business in the crankcase.
Hard to forget to close it all up with the oil door open.
 
I've been doing this for years. If you look inside any A65 or O200 Continental the dipstick tube, cap, and upper part of the dipstick tend to rust if you don't do this.
 
I would think you are having some serious moisture problem if the oil is white and foaming. I have never seen that in a normally operated engine, but I do live in a fairly dry climate.
 
I can tell you from a personal friend's experience that a 4-cylinder Lycoming will operate fairly fine with the dipstick missing. This friend added oil and was interrupted by a Gomer and forgot to re-install the dipstick. He went on a hour flight with an angle-valve IO-360 and had the same oil level as he filled to (5qts) when he discovered the dipstick back in the hangar. I wouldn't have believed it but I saw it with my own eyes. Just sayin'....
 
Amount

It’s not like the sump oil itself was milky . nasty .. Just some at the top of the dip stick cap itself ..

I think the only reason why I saw the milky white oil was that the oil had just been changed . Nice honey colored with a bit of moisture and I could see it clearly ... After a few hours ., with the oil darkened up .. would be much harder to see .

And with all the spare time we all have .. Why not play humidity games.. waiting on $49 humidity monitor..



Also should add.. This is a IO540.. so the oil filler is at the very top of the engine... Easy vented...

Venting is not going to happen as easily with and IO360 .. because of the dip stick design/location..



I always do a standard aircraft inspection before every flight.. Control surfaces...

Drain and stick fuel tanks.. Check for bird nests.. and of course oil ..

So leaving the dip accidentally out.. Will not happen..

(Well. Should not happen.. :> )
 
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The problem I have always had with this is that I cant stand around long enough to fully vent it, and if I leave the dip-stick open I forget to come back later and close it...

I'm not picking at you but don't you do at least a quick pre-flight before the next flight?
 
Yes.. There is no way you would want to leave an engine heater on with a “Sealed-Up” engine.. The moisture just able to circulate inside the crank case. Rust.. Rust ..Rust...

Be careful about making blanket statements. Some pilots run the engine heater 24/7 during the winter with the dipstick in place. That has been my practice for the past 19 years with the RV-6 and there have been no indications of corrosion.

If you wish to handle your engine as you described...fine. But please be advised other methods have been used successfully.
 
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I was watching a youtube flying video and someone commented that this sludge buildup on the oil filler neck was definitely not right. Is this what happens with the condensation inside the engine? I'm new to aircraft engines and trying to learn what to look for. This was on a Beech 6 cyl by the way. Sorry for the crappy pic.
20200429-104005.jpg
 
I would think you are having some serious moisture problem if the oil is white and foaming. I have never seen that in a normally operated engine, but I do live in a fairly dry climate.

Sorry, but a dry climate has nothing to do with it. The engine combustion produced a high water content. And combined with sulfur in the fuel condenses through out the engine crankcase.

I am now working on a purge phase using a mattress inflator. Calculations confirmed with data indicate 3 min will yield ambient moisture content in the crankcase. A 3-5 liter/min flow through a desiccant will replace the ambient moisture with very dry air in 30 min, but for safety 60 min is recommended. Doing this does not require recirculation. A quart of desiccant should not need regeneration for months, and is not contaminated by oil.

To the OP - yes that helps and should be done, but a purge with mattress inflator, or vacuum cleaner for 3 min will complete the process.
 
The only time I have ever seen moisture in the filler neck is when the oil temperature was very low on a flight before I added an oil shutter. Seems to me if the oil temp is hot enough and the flight is sufficient to burn off any moisture it would not be visible? I am in northern Ca and we dont get the severe cold in the winter
 
I'm not picking at you but don't you do at least a quick pre-flight before the next flight?

Yes, but that is not my concern. I do not want the dipstick sitting open all of the time. Would you poor a quart of oil into your engine that sat in your hanger with no cap on it for a year?
 
Sorry, but a dry climate has nothing to do with it. The engine combustion produced a high water content. And combined with sulfur in the fuel condenses through out the engine crankcase.

I am now working on a purge phase using a mattress inflator. Calculations confirmed with data indicate 3 min will yield ambient moisture content in the crankcase. A 3-5 liter/min flow through a desiccant will replace the ambient moisture with very dry air in 30 min, but for safety 60 min is recommended. Doing this does not require recirculation. A quart of desiccant should not need regeneration for months, and is not contaminated by oil.

To the OP - yes that helps and should be done, but a purge with mattress inflator, or vacuum cleaner for 3 min will complete the process.

Bill - please do share details of this device when you have had a chance to run it. I'd like to do something similar - plug it in after flight with the device on a timer that shuts it off after the engine is purged.
 
I can tell you from a personal friend's experience that a 4-cylinder Lycoming will operate fairly fine with the dipstick missing. This friend added oil and was interrupted by a Gomer and forgot to re-install the dipstick. He went on a hour flight with an angle-valve IO-360 and had the same oil level as he filled to (5qts) when he discovered the dipstick back in the hangar. I wouldn't have believed it but I saw it with my own eyes. Just sayin'....
My friend did this just the other day, with negligible oil loss and only a little oil streaking from the oil filler door after landing. My friend thinks most of the "splashing/leaking" happened after landing, when his taildragger taxiied in.
My friend will now devise a dipstick clip to the door so he won't put the dipstick in the forward baggage compartment again.
 
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My friend will now devise a dipstick clip to the door so he won't put the dipstick in the forward baggage compartment again.

The answer is even easier than that; when you remove the dip stick, just wipe it off with a rag or paper towel, then lay it on the wing walk where you have to see it when you get in the airplane! If you get in the airplane with the oil dip stick on the wing walk we'll change your name to "Indiana Jones!" :D

-Marc
 
I was watching a youtube flying video and someone commented that this sludge buildup on the oil filler neck was definitely not right. Is this what happens with the condensation inside the engine? I'm new to aircraft engines and trying to learn what to look for. This was on a Beech 6 cyl by the way. Sorry for the crappy pic.
20200429-104005.jpg

It depends on the oil you use. The white sludge you see in your photo is what I use to see when I ran Exxon Elite. I would find some on the dip-stick and sum under the valve covers. That oil was formulated to do this in the presence of moisture.
 
Sorry, but a dry climate has nothing to do with it. The engine combustion produced a high water content. And combined with sulfur in the fuel condenses through out the engine crankcase.

I am now working on a purge phase using a mattress inflator. Calculations confirmed with data indicate 3 min will yield ambient moisture content in the crankcase. A 3-5 liter/min flow through a desiccant will replace the ambient moisture with very dry air in 30 min, but for safety 60 min is recommended. Doing this does not require recirculation. A quart of desiccant should not need regeneration for months, and is not contaminated by oil.

To the OP - yes that helps and should be done, but a purge with mattress inflator, or vacuum cleaner for 3 min will complete the process.

Thanks for the data Bill, based on your description, I'm invisioning your doing the following.
Are you using a 120 volt blower?
I have used Duck Bill valves in the past and they may work well in this application as check valves.

oCv.jpg
 
Question

I like this design and idea. I have a question. Would it be better if it was a closed loop cycling air within the engine so not to have to remove the humidity from the ambient air constantly? Just a thought.
 
I like this design and idea. I have a question. Would it be better if it was a closed loop cycling air within the engine so not to have to remove the humidity from the ambient air constantly? Just a thought.

No - why?? Here is why.

1. The objective is to replace the air in the crankcase with dry (low dew point) air.
2. The mixture after shutdown in the crankcase measured as lbs water/lbs dry air is many times higher than ambient.
3. The run time to replace the crankcase air to a 99% certainty is the same in either case.

So, if the crankcase volume time is know for a particular system, then simply use a timer and then shut off the desiccant system.

Make sense?

Thanks for the data Bill, based on your description, I'm invisioning your doing the following.
Are you using a 120 volt blower?
I have used Duck Bill valves in the past and they may work well in this application as check valves.

Well, yes, basically Don, but the break pressure on check valves I could find was too high, so at the moment I have some 3-way valves. I would sure like to use a low opening pressure check valve with the configuration you showed. So Please, tell me more about this Duck Bill valve. I can imagine how it works, like the reed block on a 2-stroke engine or the back flow plates on the V-1 buzz bomb? But where can I get some?

The forward pressure of the aquarium pump is not very high so a valve must seal on it's own and not leak. A different design air pump could be needed to handle higher pressures. These are reliable and low cost.
 
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Scuba dive shop

You might find a valve at a scuba dive shop. Some snorkels have these low pressure air valves.
 
Well, yes, basically Don, but the break pressure on check valves I could find was too high, so at the moment I have some 3-way valves. I would sure like to use a low opening pressure check valve with the configuration you showed. So Please, tell me more about this Duck Bill valve. I can imagine how it works, like the reed block on a 2-stroke engine or the back flow plates on the V-1 buzz bomb? But where can I get some?


A Duckbill valve has an extremely low cracking pressure and seals very well against back flow. Most are made of Silicone rubber and are widely used in the medical and some food related applications.
Amazon has them listed for replacement parts for Breast pumps. Example here:

My experience has been with valves produced by Vernay, link here
 
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A Duckbill valve has an extremely low cracking pressure and seals very well against back flow. Most are made of Silicone rubber and are widely used in the medical and some food related applications.
Amazon has them listed for replacement parts for Breast pumps. Example here:

My experience has been with valves produced by Vernay, link here

It sure looks like I have some more component development to do, and this looks very promising! Forward pressure drop, and cracking pressure along with back leak will all have to be measured to ensure the performance remains. I am also looking at a paper element inline fuel filter for the final control of contaminants getting into the engine. Thanks.

For short trips, less than a month, a battery powered purge design is also in the works. No drying action just a 3-5 min blast with a separate battery to prevent any condensation, same 5 min mechanical timer. Hook it up upon exiting the aircraft, store gear, gust locks, etc, then remove and restore the dipstick before leaving the ramp/hangar.
 
It sure looks like I have some more component development to do, and this looks very promising! Forward pressure drop, and cracking pressure along with back leak will all have to be measured to ensure the performance remains. I am also looking at a paper element inline fuel filter for the final control of contaminants getting into the engine. Thanks.

This valve would work down stream of the aquarium pump.
I have tested it with the small flow meter you listed and show 2 liters/ min flow with it inline, no flow reduction.
 
Spitballing here but I wonder if a PCV (Positive Crankcase Ventilation) valve from a car would work? I remember replacing one in my Civic many years ago and I recall it didn't take much pressure to get it to move.
 
How about a 2 min shot of shop air in the breather, dipstick open, postflight?

Can you flush enough saturated vapor with fresh air to make a difference?

Lots seem to open the dipstick.
Lots use Camguard.
Some use an air drying system.

In any of the cases, would a fresh air flush make a measureable difference?

Keep a closed loop cleaner, give longer between bakes for open and closed loop silica gel? Best if oil at or above 150/180/?
 
How about a 2 min shot of shop air in the breather, dipstick open, postflight?

Can you flush enough saturated vapor with fresh air to make a difference?

Lots seem to open the dipstick.
Lots use Camguard.
Some use an air drying system.

In any of the cases, would a fresh air flush make a measureable difference?

Keep a closed loop cleaner, give longer between bakes for open and closed loop silica gel? Best if oil at or above 150/180/?

1. My calculation for a 4 gal crankcase cavity, assuming instant dilution for each cc entering, is it will take 145 liters of air to replace the interior volume to less than 1% of original content. A "fresh" air flush is the same as an ambient purge. (?)
2. The only purpose behind the "purge" is to prevent any possible condensation as the blow-by assumed to have dew point around 180F. I have been too lazy to do the combustion calculation for water density relative to dry air and compare to the steam tables.

So- IMO yes an air compressor blast would work. Must be filtered though. And - the only reason I can fathom for a continuous dry air system is the possibility for condensation that will take time to evaporate. In theory, assuming my calculations are correct, a 3 L/min dry air supply will reach 99% purge in 30 min but would leave it on for an hour.

Although the 3 min purge did yield ambient humidity in the exit stream at the end (and semi-validated the calculation), I have not tested the dry-30min-3L/m stage.
 
Caution with air source

As has been mentioned earlier,.... need to be careful you don’t put some bad stuff in, while you are trying to get the air dry in the crankcase. I would NOT use blast from compressed air or a air blown from a vacuum cleaner.
 
Desiccant

No - why?? Here is why.

1. The objective is to replace the air in the crankcase with dry (low dew point) air.
2. The mixture after shutdown in the crankcase measured as lbs water/lbs dry air is many times higher than ambient.
3. The run time to replace the crankcase air to a 99% certainty is the same in either case.

So, if the crankcase volume time is know for a particular system, then simply use a timer and then shut off the desiccant system.

Make sense?



Well, yes, basically Don, but the break pressure on check valves I could find was too high, so at the moment I have some 3-way valves. I would sure like to use a low opening pressure check valve with the configuration you showed. So Please, tell me more about this Duck Bill valve. I can imagine how it works, like the reed block on a 2-stroke engine or the back flow plates on the V-1 buzz bomb? But where can I get some?

The forward pressure of the aquarium pump is not very high so a valve must seal on it's own and not leak. A different design air pump could be needed to handle higher pressures. These are reliable and low cost.

Hi Bill. The reason for the suggestion is that I had a similar system setup that I discovered online as a DIY system using the aquarium pump. I ended up having to dry out the desiccant often (once a week) as it was sucking ambient moisture into the system. My thought was a contained loop may cycle dry air without having to dry out the desiccant as often.
Just a thought.
 
Sounds to me like you've got bigger problems than you think. I actually went back and read the original post. You've got big problems if you run your engine at operating temperature and at shut down you've got steam coming out of your oil fill tube. Operating temperature should dissipate any and all moisture in your engine, that is condensates. If you've got steam coming out of your filler tube, I imagine you've got problems with corrosion.
 
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Hi Bill. The reason for the suggestion is that I had a similar system setup that I discovered online as a DIY system using the aquarium pump. I ended up having to dry out the desiccant often (once a week) as it was sucking ambient moisture into the system. My thought was a contained loop may cycle dry air without having to dry out the desiccant as often.
Just a thought.

Al, here is a psychrometric calculator to use relative humidity or T-dp to calculate the water in the air.

If we assume a 3 L/min flow, ambient of 90F with 90% humidity, 60 min run time where the initial (post shutdown) water density in the engine is assumed to be 4553 grains/lb dry air. @ 90F/90% it is 86 grains/lb, dry. This is 53X the ambient humidity.

If recirculated, then it will have to take that rich water laden air and adsorb all the water. If open loop it will dry the 90/90 air. Lets assume all the water is removed it each case.

The crankcase volume is 16L. Pump flow at 3 L/min and 60 min operation will flow 180 L. That is 2X the calculated crankcase replacement time. 180/16=11.25

Using a crude ratio instead of a calculated absolute water weight, 53X water ratio vs 11.25X volume ratio tells me that the desiccant would adsorb much less water per engine operating cycle during 60 min operation in open loop than closed loop.

Sorry for lots of numbers, but this is the comparison that led me to this conclusion. And - - the desiccant is not contaminated with oil vapors, a problem I consider to be unacceptable for long desiccant life.

If used open loop with unknown flow rate, and no timer, then the desiccant saturation would clearly happen more quickly as in general experience.

Edit: If the crankcase is purged, then a closed loop system is installed and run for an hour then the desiccant life would be 10X longer than open loop.
 
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That's funny. I flew my 8 yesterday---ECI IO 360---no steam at all afterwards.:confused:

Me too. No visible steam exiting the open tube. OAT was 78F, so maybe just not condensing enough to be visible. Looking down into the tube with a flashlight, there was fog of some kind, but I could see all the way to the bottom of the tube.
 
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I don't get it...

Lycoming put a vent on the engine to remove moisture and relieve pressure in the crankcase. Why do you need to open up another hole? If you have moisture in the crankcase after flying, you didn't fly long enough to fully atomize the moisture. Fly more!
 
I?m with you Ron. I?m wondering if this discussion would be happening if we weren?t laying low because of corona virus. Can?t fly (well, some of us can, and do), and we?re bored. It was a nice day yesterday here in OH and I flew twice yesterday - no moisture from the tube either time.
 
Some data

Ya.. this thread would not be happening in normal times..
It’s just fluff..
Typ Operation..
2+ Hour average flight times...
180-185 oil temps
Got to remember air temp 35-40F here.. Easy to see water vapor

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