The International Cessna^® 170 Association

Is the C-145 more prone to "making" H2O than other engines? I noticed today when I opened the oil filler that there is lots of condensation in the cap along with some rust / corrosion in the filler tube itself. This was this afternoon prior to flight; we flew yesterday for nearly 2 hours. Temps were warm enough to boil off water (I think!)
My IO-360 skyhawk is always dry as a bone - I never see any moisture anywhere in the engine, and the oil analyses have always had low moisture content.
Is this common? If not, what (if anything) should I do about it? I have also noticed that the few drops of oil that come out the breather tube onto the hangar floor after flying are mixed with water...

Thanks
Thomas

Moisture in the engine is primarily from two sources: Condensation and Combustion (of fuel.)
The majority of water is due to the byproducts of burning hydrocarbon fuels. The major byproducts are: Carbon dioxide, Carbon monoxide, and water vapor ("hydrogen monoxide".) (Lots of lesser byproducts are also created like nitrous oxides, nitric acid, bromic acid, sulfurous and sulfuric acids, etc. etc..)
The majority blows out the exhaust. A little gets past the rings and into the crankcase/sump.
When the engine cools down (due to shut-down, or descents under lower power, or thru cooler air, etc.) any water vapor present in there can condense, and a lot of that ends up in the oil, where it can cause rust and mix with those acids where it can cause corrosion. Since the oil remains hot for some time after shut-down, any water in that oil is driven out into the airspace above the oil level. As the metal cools down, that vapor can condense onto the walls and in the tube.
After the engine cools, the air inside the sump also contracts.
This sucks in additional atmosphere...which probably also contains water vapor. So,... yes, lots of potential for water vapor in the crankcase exists...in all models of engines.
As for why your O-300 seems to display more of it than your IO-360,... the answer probably lies in the actual location of the oil filler cap. The IO-360 sits on top of the engine where it remains fairly hot for a long time after shutdown. In fact, it probably has an increase in temp for a short period due to lack of cooling air, and rising heat from the engine below it. Plus it's a shorter tube, and any water vapor available will have lesser reason to condense on such a small area, espeially one that remains hot due to it's location. Any such water will likely drain directly into the lower areas of the engine.
But the O-300 oil cap (and filler tube) is located in the low pressure area of the cowling, and away from the main body of the engine, and in that area receives considerably less residual heat than it's counterpart in the IO-360. It's also a much longer tube, and therefore has a greater exposure to airflow and therefore greater variation in internal temps along it's length. (The bottom of the tube, being in more direct contact with the engine would be warmer/for a longer period of time, than the upper end of the tube. This would probably be conducive to greater condensation of available moisture, especially along the upper end of the tube near the cap.
So, I doubt that the O-300 has any inherent reason to make more water vapor, but I suspect it's actual oil filler tube design and location are more to blame for the appearance of more water.

The filler on the 360 is plastic ... that could also make a difference in the amount of condensation.
However, the filler on the 360 is also outside the high pressure part of the cowl and is really away from the engine / case; it seems to me like the filler on the C-145 is shorter (although I am not as familiar with that engine so I don't have a great picture of it in my head).

I guess I'm wondering if others have experienced similar stuff and / or if there is anything I can / should do about it.

Thanks!
Thomas

When we talk about the IO-360 engine in Cessna 170's, we are usually referring to the TCM engine. When you mentioned "Skyhawk", I thought of the Lycoming engine series installed in later Cessnas, where the oil filler tube is located directly above the crankshaft. My bad.
http://www.pennyanaero.com/engines1.asp ... &x=13&y=10
The TCM oil filler tube is installed as you described, but I still don't believe the O-300 makes more water than the IO-360. I would think the greater fuel consumption rate of the IO-360 should equal greater water-vapor production.

gahorn wrote:The major byproducts are: Carbon dioxide, Carbon monoxide, and water vapor ("hydrogen monoxide".)

George, I'm sure you meant dihydrogen monoxide, very toxic.

http://www.snopes.com/science/dhmo.asp

Ha! Actually when I wrote the original post, after typing in hydrogen-monoxide, I realized that my High School chem teacher would scold me for not correctly noting the two hydrgen molecules attached to the single oxygen molecule, (H2O) and thereby offering the nomenclature DI-hydrogen... but at that point I was off to other projects and considered any correction unnecessary for the discussion. (I should have been thinking of the correct engine mfr instead, No?)
Urban legends is a great site. If political arguments were always researched there before "hot topic" emails were fired off to others, ...there'd be a lot less anger in the world.

tshort wrote:Is this common? If not, what (if anything) should I do about it? I have also noticed that the few drops of oil that come out the breather tube onto the hangar floor after flying are mixed with water...

As far as commonality, I think the answer is yes. I've seen the same conditions with all of the small Continentals I have owned.

gahorn wrote:When we talk about the IO-360 engine in Cessna 170's, we are usually referring to the TCM engine. When you mentioned "Skyhawk", I thought of the Lycoming engine series installed in later Cessnas, where the oil filler tube is located directly above the crankshaft. My bad.
http://www.pennyanaero.com/engines1.asp ... &x=13&y=10
The TCM oil filler tube is installed as you described, but I still don't believe the O-300 makes more water than the IO-360. I would think the greater fuel consumption rate of the IO-360 should equal greater water-vapor production.

George, what are you trying to illustrate with the above link? The picture I get at this link is neither a Lyc nor TCM IO-360. It's a TCM IO-470 or IO-520, not sure which. All of the TCM IO-360's I've seen have separate rocker box covers for each valve, that is, two per cylinder. Somewhere there's TCM documentation on the major dimensions and features of the various TCM engine models, but I've not been able to relocate it.

Miles

Hmmmn.. The link showed a different engine when I first clicked on it. When I returned to the site, it has varying engines being displayed.
Poor illustration for me to have selected for use, I guess. Anyway, the engine I had in mind, is clearly not the one originally being discussed, but it's of little import I think.
None of these engines would be likely to generate more moisture than another in similar service, was the point I meant to make.

I have noticed that all the TCM engines in our company aircraft (and my own O300) make more water than the Lycomings. You can tell it by looking in the fillers, by what comes out of the breathers, and by the color of the oil. The TSIO 520's especially turn their oil green, while Lycs always turn oil black pretty quickly.

Ben Visser (former Shell Oil guru) said that their experience was the same, and he was the one who explained the oil color difference and meaning.

My O300 breather always leaves little drops of oil/water sludge on the hangar floor after flying, and it has always done so no matter what the compressions were at the time.

gahorn wrote: None of these engines would be likely to generate more moisture than another in similar service, was the point I meant to make.

HA wrote:I have noticed that all the TCM engines in our company aircraft (and my own O300) make more water than the Lycomings.

Could it be that all engines "make" similar amounts of water (at a rate possibly proportional to fuel flow), but some get rid of it better than others? Just thinking out loud...

For the "what can I do about it?" question, note that there are TWO oil drains in the bottom of the C-145/O300 sump. There's one just ahead of the carburetor mounting boss as well as the main one toward the rear. Due to the internal casting configuration of the sump, moisture/acid-laden oil can get trapped in the area of the front drain. It's not uncommon to see sumps that have corroded all the way through in that area. It's rather a pain in the hindparts to pull the front plug due to the proximity of the carb air box and engine mount, but it's a very good idea to occasionally do so to ensure complete drainage.

Miles

that is a fine observation there Miles, and since I am about to annual my trusty steed I will pull that plug and report my results

Hans

tshort wrote: Is this common?

Thanks
Thomas

Thomas, Mine also makes a lot of water, has lots of rust under the filler cap, and always has a fresh pile of frozen condensate on my engine blanket (below the breather tube) the next day when flying in freezing temps.

Mine has always looked like that too. It looks troubling until you find out that nearly everyone has the same thing going on in thier oil filler tube. If it's been that way for 50 years then I suppose it will be OK for another few years

I sorta figured it wasn't a big deal.
My buddy Stu (the CFI/A&P/IA who is working on my TW endorsement with me) said no biggie. He has had his C-140 for 20+ years and said his rusted to the point where the tab broke off the filler cap and he had to replace it.
He was giving me a hard time the other day when I changed the oil in my skyhawk at ~30 hours (5 months - winter this year has been bad for flying!) ... the oil analysis looked good and he said "next time you drain good oil like that out of your engine just bring it on over and I'll use it for a while in mine!"

Thomas