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White steam/smoke from oil filler tube after flight

prkaye

Well Known Member
After a flight today with ambient Temps about -2 Celsius, I took the oil cap off so that I could connect the engine dryer (it connects to the oil filler tube with a tube through a rubber stopper). When I took the oil cap off I noticed significant visible amounts of white-ish steam or smoke coming out of the oil filler. Oil Temps and pressure during flight had been normal, except for a brief spike of oil pressure to about 92 earlier in the flight.
I assume that what I saw coming from the oil filler tube after the flight was just steam from the warm air in the engine suddenly hitting the cold ambient Temps, but I wanted to ask here if there is anything about this that should concern me?
 
Product of combustion

After my first oil analysis where done (Blackstone) they were reporting a small water amount (Never said it was an issue) and a friend recommended loosening the cap after flight. I got in the habit and yes would see a small amount of water vapor coming off and after I started doing that my water content for the oil analysis would come up zero. Recently another friend thought it might be possible for the small lizards that live in our hangars to climb down the now slightly open oil tube. At first, I blew the thought off but just today I drilled 4 - 0.125-inch hole one thread below the O-ring. Now I just open and let the dip stick sit on the cap. Lizard safe........
 
product of combustion

product of combustion
Yes, water is a product of combustion, but why would these products of combustion be in the oil sump? Shouldn't they be blown out the exhaust ports?
 
Temp of oil

Hopefully someone more knowledgeable than me can provide input but from what I understand one of the reasons we like to get our oil temps in the 180 - 200 range is to blow off the water that gets in our oil. It does not need to get to 212 for this to occur and 180+ is ok. Bottom line, it's normal to see water vapor and someone else can provide a better response than me why.
 
Perfect ring sealing would prevent this. That anin’t gonna happen. Oil can/does absorb water from the ambient after the engine cools. Worse in humid environments where the ambient has big deltas over time.

One of the reasons ground running an engine is bad for it, the oil doesn’t get hot, long enough to boil off the water (among other things). Short flights can also be bad. You’ll hear different times but a good rule of thumb is 30 minutes after the oil has reached operating temp. Would be very interesting to from the previous posters; does the amount of steam witnessed from the oil fill port vary with flight duration?

Edit for dmatmul. True. The local temps get much higher than the measured bulk temps.
 
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Ring blow-by gasses. The ring seal is good, but not perfect. Carbon, exhaust and byproducts of combustion, including water, pass the rings and into the crank case. This includes the oil that's in the crank case. It's why crank cases need a breather tube too; to vent the blow-by gasses.

An interesting story from my days in flight school. We had two aircraft freeze the breather tube shut from the water vapour in the blow-by gasses. The pressure built up in the crank case and blew out the front crank case seal. Oil all over the place. One aircraft landed on a frozen lake!
 
Ring blow-by gasses. The ring seal is good, but not perfect. Carbon, exhaust and byproducts of combustion, including water, pass the rings and into the crank case. This includes the oil that's in the crank case. It's why crank cases need a breather tube too; to vent the blow-by gasses.

An interesting story from my days in flight school. We had two aircraft freeze the breather tube shut from the water vapour in the blow-by gasses. The pressure built up in the crank case and blew out the front crank case seal. Oil all over the place. One aircraft landed on a frozen lake!

Most certified planes have a hole that is deformed a little and looks kinda like a whistle in the breather tube inside the cowl perhaps a foot or so from the end. That’s to prevent exactly that situation. The whistle part won’t vent vapors when the tube is working properly, but when the end gets clogged or frozen, the whistle part is still within the warm air of the lower cowl. Perhaps someone thought the tube was damaged and “repaired” it by installing a new tube without the second hole?
 
An interesting story from my days in flight school. We had two aircraft freeze the breather tube shut from the water vapour in the blow-by gasses. The pressure built up in the crank case and blew out the front crank case seal. Oil all over the place. One aircraft landed on a frozen lake!

Most certified planes have a hole that is deformed a little and looks kinda like a whistle in the breather tube inside the cowl perhaps a foot or so from the end. That’s to prevent exactly that situation. The whistle part won’t vent vapors when the tube is working properly, but when the end gets clogged or frozen, the whistle part is still within the warm air of the lower cowl. Perhaps someone thought the tube was damaged and “repaired” it by installing a new tube without the second hole?

It's in the RV construction manuals:

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A Question

Do you have an inverted oil system.
Personally I’m not a great fan of these, for the reason they do not get rid of the moisture in the crank case efficiently enough.
In my opinion they are fine if you are doing hard aerobatics frequently.

Just my 2p worth.

Rob
 
Hopefully someone more knowledgeable than me can provide input but from what I understand one of the reasons we like to get our oil temps in the 180 - 200 range is to blow off the water that gets in our oil. It does not need to get to 212 for this to occur and 180+ is ok. Bottom line, it's normal to see water vapor and someone else can provide a better response than me why.

Yes, this is normal. The air inside the crankcase is fully saturated with as much moisture and it can hold. As mentioned, the blowby gasses contain considerabl amounts of H2O. Unclear if it is in visible steam form in that case. However, once you expose that air to the substntially cooler ambient air with it's lower dew point, it will create visible steam as the mixing of air parcels causes the dew point to drop and forces the water to become visible as steam. The exact same process that forms cumulus clouds at the condensation layer

Larry
 
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Pulling the dipstick out after a flight (especially a short one) is something I try to remember to do to help get the moisture out of the crankcase.
 
Pulling the dipstick out after a flight (especially a short one) is something I try to remember to do to help get the moisture out of the crankcase.

I think Ed Kollin of Camguard fame said when asked about this practice, "it can't hurt". I too see visible moisture coming out when I open it after a flight.
 
I pull the dipstick out after a flight, short or long.
When I don't or forget to do it, I almost always see droplets of moisture on the dipstick on the next preflight.
That, even if I keep the oil temps 180+ during flight.
I have the AeroSplat Breather Seperator installed.
It's obviously not blocked as I do have a few drops of oil dripping from the big hose on the to the exhaust tip.
 
I to pull the dipstick and wrap a rag around the end (so it doesn't fall back into the hole) and leave the door open.
My plane lives in a dry fully insulated hangar, so it's kinda babied.
Being a mechanic for 55 years leaves me with experience of yester year.
I've seen many a car (50 years ago) that had pasty, whitish oil crud on the breather cap, and in the whole engine if we tore them down for some reason.
Because, the people only drove short trips and never really got the engine up to temperature for long enough.
Saving gas and ruining the engine.
To many people do this with aircraft engines.
I always close the oil cooler door till the temperature gets up to at least 180 or close it to keep the temperature up in cruise at cold temperatures.
Water is a product of combustion and you need to get rid of it. I burn Costco premium with that dreaded Ethanol.
Look at the back of any running car and you will see water running out of the tailpipe. That's why the exhausts are made out of Stainless steel on todays cars.
Of course if you have to keep the aircraft outside it's a different story.
Hey! How about pulling the dipstick and putting it on the seat.
You won't forget to put it back in for sure.
My three cents worth Art
 
It would work a lot better if you opened up the vent line at the top of the motor.
Your vent outlet is lower than the motor and will trap the hot moist air up where the cam,
crank, and cylinders live. When you pull the dip stick, you vent only the sump...
because hot air rises. But, it's better than nothing.

The dip stick and plastic holder are two of the first parts of the motor to cool down and collect moisture.

As you know, you can crack open the the door on your dishwasher right after the rinse and steam will
escape and the dishes will dry in 30 seconds.
 
I plug the dehydrator (aquarium air pump) into my dipstick tube right after a flight. Some guys go so far as to hook up a pool-toy inflator for a few minutes to exhaust the bulk of the moisture-laden air, then hook up the dehydrator. I don't do that, but I think this is an interesting idea.

pool toy inflator
...Hi/Low -- 300-150 L/Min. That oughta do it.
 
No concern, normal.

After a flight today with ambient Temps about -2 Celsius, I took the oil cap off so that I could connect the engine dryer (it connects to the oil filler tube with a tube through a rubber stopper). When I took the oil cap off I noticed significant visible amounts of white-ish steam or smoke coming out of the oil filler. Oil Temps and pressure during flight had been normal, except for a brief spike of oil pressure to about 92 earlier in the flight.
I assume that what I saw coming from the oil filler tube after the flight was just steam from the warm air in the engine suddenly hitting the cold ambient Temps, but I wanted to ask here if there is anything about this that should concern me?

The combustion chemical equation shows there is a lot of water produced. The crankcase is filled after a flight with blow-by which is primarily combustion gas, thus the water condensation coming from the oil fill tube.

I made some engine dryers for my friend and I, and he noticed that water accumulated rapidly in the recirculation tube on a cold day. He measured 4-5 tablespoons in the first 10 minutes.

As a result, I made (new design) with a high flow purge cycle for my dryer. It runs for 5 minutes and calculations would indicate it purged 99% in 3 minutes at 20L/min. I run it for 5 min then switch to desiccated air at 2.5 l/min for an hour. The purge reduces the chance for rapid engine cooling to condense water into the oil before the low flow can lower the crankcase dew point below the engine temp. The method greatly extends the desiccant life and won't stink when regenerated like a recirculation configuration.
 
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As a result, I made (new design) with a high flow purge cycle for my dryer. It runs for 5 minutes and calculations would indicate it purged 99% in 3 minutes at 20L/min. I run it for 5 min then switch to desiccated air at 2.5 l/min for an hour. The purge reduces the chance for rapid engine cooling to condense water into the oil before the low flow can lower the crankcase dew point below the engine temp.

There ya go....the pool-toy-infllator paradigm. It's an intriguing concept. Exhausting all that moisture-laden crankcase air would save on the amount of water that my dehydrator has to absorb, and thereby decrease the amount of work that my wife puts into drying my dessicator beads every couple of months.
 
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