Taking the Dipstick out after a flight?

SixPapaCharlie

SixPapaCharlie

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In the last few weeks, randomly it has come up twice that I should remove the dipstick after a flight and let the vapor escape.

I was told "for every gallon of AvGas burned, a quart of water is created inside the engine."

The water vapor rises to the top of the engine and sits there on the surface doing what water does inside the engine. It was explained to me the best thing I can do to increase the life of my engine is let this vapor out.

My last 2 flights, I opened the oil door, and removed the dipstick, and sure enough for about 15 minutes, water vapor rose out of the oil filler tube like smoke out of a chimney.

Do you do this?
Is it bad if I don't do this?

It is new information and I am curious if others agree that we should be letting the vapor out this way so it doesn't condense and corrode the top bits of the motor.
 
I do it, been doing it for years in rental cirrus. Always amazed at how much steam comes out of that filler.
 
I do it too. I’m not sure how much I’m accomplishing by it, especially since it has a breather tube, but I have made it into a post shut-down routine.
 
Same here.

And I leave the dipstick ajar post flight when in low humidity desert climates, with the oil door ajar as well as a visual indicator for me.

Intent is to let the remaining water and vapor continue to evaporate over time while sitting.

It gets screwed back in when I check the oil level at the next preflight.

I’ve not send data to support extended engine life, but intuitively it makes sense for me.
 
New pilot here, haven’t heard that one yet, but I have not been doing that.
 
I’ve done it a few times, usually not though. I’m kinda neutral on the idea & process, nothing against it. I would want the dipstick to be at least lightly in place when I leave the aircraft, don’t want to forget it. Of course oil level gets checked before every flight.


Maybe I should start doing it again? Yes, I’d rate routinely flying the craft as higher priority.
 
Checkout_my_Six said:
Never done it.....I've owned airplanes since the 80's....It hasn't made a difference. Flying it regularly helps more.
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Our A&P is a fan but given our plane gets 200 hours a year on it (and has a plug in heater for winter ops) I can't see that it does anything other than provide another entrance for moisture when the engine is cool.
 
When I return to the hangar after a flight I loosen the dipstick and leave the oil door open as a reminder. Once the plane is clean and secure the last thing I do before locking up the hangar is tighten the dipstick. Of course as Six mentioned "Flying it regularly helps more".
 
@SixPapaCharlie aren't you in sort of a 3 sided shade hangar with no door? In that case I'd be more worried about what's getting IN the dipstick hole than what it allows out.

I used to do it, but it's kind of a pain so I quit. In the winter my vent tube will condense maybe an ounce of water... I'd guess that's about the amount that would exit through the dipstick tube. Probably not great to have that inside the engine, but I'm sure that's only a small percentage. As long as you fly every week or two the engine won't rust. If you are really paranoid about water in the engine you should get a dehydrator and hook it up every time.
 
When o do ot, it isn't for more than 10 or 15 minutes usually, then it gets buttoned up. I leave the oil door open. If I'm getting lunch I'll leave it open while I eat. I think it makes a difference. On days I forget, there is a surprising amount of condensed water in the filler tube when I check the oil after the engine has cooled. Ymmv.
 
I don’t bother. It seems to me the amount of steam you’ll get is such a small fraction of the water in the engine that it just won’t matter much. I have been considering a dehumidifier of some sort, though.
 
undip the dipstick, interesting
 
Yeah, I've gotta say in all my years of being around engines and industrial machinery I've not heard this one....
It might actually be interesting to see analysis done on this...it would be a good one for that old TV show Mythbusters.

I wonder...how much of the released vapor you are seeing/detecting is actually water?
Is anything else from the oil or additives being released that shouldn't be?
Of the total water vapor in the engine, how much is released? How much remains?
As the engine cools, is anything being drawn in? Ambient humidity for example?
Difference in opening it up vs just leaving the crankcase vent to do it's thing as the engine manufacturer engineered it?

My gut says that the outcome MIGHT be "plausible"... and not likely "confirmed". Probably not enough of an improvement to be measured...

SixPapaCharlie said:
......
I was told "for every gallon of AvGas burned, a quart of water is created inside the engine."
.......
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if that 1 quart number is true, then I would guess approximately 0.9999988769801 quarts gets blown right out the tail pipe
 
Probably doesn't do much of anything in reality, but it doesn't "hurt" anything, either. As long as you don't forget to button it up before the next flight you should be fine.
 
Half Fast said:
I don’t bother. It seems to me the amount of steam you’ll get is such a small fraction of the water in the engine that it just won’t matter much. I have been considering a dehumidifier of some sort, though.
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That there. It would take a lot of that visible "vapor" to make a drop of water.

Burning agallon of gasoline can create as much as a gallon and a half of water, the vast majority of which goes out the exhaust, even when the engine has just been started and is warming up. A bit of it gets past the rings and condenses in the case, but get this, folks: there is oil flying around in that crankcase, coming off the crankshaft and rods and everything, and it splatters on the case walls and mixes with that water and forms an emulsion, the brown goop you see on the hangar floor after a short flight in colder weather. The water is so mixed into the oil that it cannot escape out of the dipstick tube, and you're wasting your time with that.

The only way to get rid of it is to get that engine up to operating temperatures and the water will come out of the emulsion and leave the engine. Getting the water hot raises its vapor pressure. It doesn't have to boil, but it might when it hits the backsides of the hot pistons. Oil temperature is at the oil inlet, not where it leaves the engine on its way to the oil cooler. With the engine hot, any water in the blowby will be ejected quickly, and when you land and taxi in, very little further water will accumulate unless you waste your time doing something with the engine idling.
 
oil is the answer.....make sure there is oil in there to coat all the parts. ;)
 
It would be clever if there was a one way valve which you could place in the dipstick hole. It would allow vapor to escape. It would have a dessicant in it so that when the valve closed, air could pass through the dessicant and fill the engine case.
 
Of only someone would invent a system that could positively ventilate the crankcase with the engine running.
Perhaps something crazy like making something called a PCV valve connected between the crankcase and intake manifold that would draw fresh air through the crankcase when you have the throttle partly closed coming in for a landing and taxiing back to the hanger / tie down. Not that something like that would ever work. I mean, whoever in the world would come up with something as stupid as that. You would never see something like that in a car... And even if you did, would it really be worth the huge increase in engine life (based on what would have happened to cars if they had put PCV systems on back in the 1960s, but of course they didn't so we will never actually know) really be worth it? They didn't have that sort of thing in the 1930s, so why would you want it now?
 
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It's an impressive amount of water. I'll try to get a picture next time I do it, the real proof is when you forget an get treated to milky oil and water droplets when checking the oil. This is on an IO-550N engine.
 
First I’ve heard of it,have had five airplanes and never did it. I’d be afraid of not tightening it back down if I got busy.
 
Capt. Geoffrey Thorpe said:
Of only someone would invent a system that could positively ventilate the crankcase with the engine running.
Perhaps something crazy like making something called a PCV valve (named by the department of redundancy department) connected between the crankcase and intake manifold that would draw fresh air through the crankcase when you have the throttle partly closed coming in for a landing and taxiing back to the hanger / tie down. Not that something like that would ever work. I mean, whoever in the world would come up with something as stupid as that. You would never see something like that in a car... And even if you did, would it really be worth the huge increase in engine life (based on what would have happened to cars if they had put PCV systems on back in the 1960s, but of course they didn't so we will never actually know) really be worth it? They didn't have that sort of thing in the 1930s, so why would you want it now?
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The PCV system relies on intake vacuum to make it work. Low MP, in other words. But an aircraft engine is running at high MP almost all the time, and the pressure differential across the PVC valve is too small to draw any significant amount of air through the case.

The RV anti-splat strut guys make a sort-of PCV system for homebuilts. It uses vacuum generated by exhaust flow. It's intended to eliminate the oil mess on the belly, but it has no air inlet for the crankcase and so it's not a true PCV system.
 
PaulS said:
It's an impressive amount of water. I'll try to get a picture next time I do it, the real proof is when you forget an get treated to milky oil and water droplets when checking the oil. This is on an IO-550N engine.
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Can someone tell my why that vapor will come out of the dipstick tube but refuses to come out of the breather? Both of them lead directly into the crankcase, with no restrictions anywhere.
 
Dan Thomas said:
Can someone tell my why that vapor will come out of the dipstick tube but refuses to come out of the breather? Both of them lead directly into the crankcase, with no restrictions anywhere.
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Dipstick points up and breather points down and hot vapor rises?

PS> I'm in the "I don't see the point in doing this" camp.
 
Law of primacy. My original CFI did not teach me to do this 22 years ago and he was a former airline pilot. I haven't worried about it and the club hasn't lost a motor due to water in the oil as long as I've been a member (22 years). YMMV.
 
Salty said:
Dipstick points up and breather points down and hot vapor rises?

PS> I'm in the "I don't see the point in doing this" camp.
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The whole idea is that the water will "boil" off while the engine is still hot. If that's true, it will escape out the breather as well as out the dipstick hole. I think the only advantage is some circulation of drier, ambient air through the case for a half-hour or so. And even that might cool the case down and stop the evaporation process sooner.

Some dipstick tubes are long enough that they're buried in the oil, and nothing can escape except oil.
 
So....maybe you could do a video on your dipstick? o_O

Throw in some special effects....and it might be cool.

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smoke-show-cannons.gif
 
Ghery said:
Law of primacy. My original CFI did not teach me to do this 22 years ago and he was a former airline pilot. I haven't worried about it and the club hasn't lost a motor due to water in the oil as long as I've been a member (22 years). YMMV.
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Given that oil is the critical link in the operation of a piston engine, I am somewhat tempted to believe this hypothesis. But I would like to know what experts like Mike Busch think about this theory. There is no reason to believe that an airline pilot would know much about piston engines.
 
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