Oil Discoloration

[CT583]

This morning I had a small puddle of oil sitting below the plane. It came through the breather tube as I added an extra quart prior to a 3.5 hour flight. My O-470 likes 9, I was at 8.5 so added a full quart and expected a little blow out.
regardless of that issue, the color seemed alarmingly off. pics attached.
however the dipstick oil looked normal.
could humidity have caused this?
Or running for 3.5 hours doing approaches and going missed?(varied power settings)

The only other item I changed was that I did add the oil to a partially warm engine. I don’t know if that’s the culprit, but I’d like some of your opinions on the matter.

Thanks.

 

[Jim K]

That's mostly water. Mine will do that when it's real cold out. I assume the moisture in the crankcase condenses and drips out after shutdown. Mine made a little brown frozen stalagmite in the drip pan this winter, which is what made me take note of it.

 

[Clip4]

Why winter preflight should include inspection of the breather outlet to make sure it is not obstructed with ice.

 

[455 Bravo Uniform]

That’s normal. The byproduct of combustion is water and CO2, and those gasses blow by the piston rings and end up in the crankcase where they mix with the oil and oil mist. The breather tube routes those gases out and fresh air back in. What you’re seeing an oil-water emulsion. If you look closely you might be able to see water droplets. I keep cardboard on the floor under my breather to catch the post flight drips. Once the cardboard gets oily, that emulsion has a hard time soaking in due to the water content in the drips (oil & water don’t mix well).

A pic of what @Jim K said about a stalagmite:

 

[CT583]

Ok, this is a new one for me. Thank you for the great insight. Learned something new.
You all rock for the replies!

the stalagmite kind of looks cool.

 

[Domenick]

I commend everyone for the proper use of stalagmite.
Looks just like the milkshake from a blown head gasket in a water-cooled auto engine.

 

[1RTK1]

He's got a blown head gasket Better get that fixed ASAP

 

[CT583]

He's got a blown head gasket Better get that fixed ASAP

Well I just sent it to the shop for an oil change.. guess I’ll find out if you’re correct. fingers crossed.

 

[1RTK1]

Have them check the muffler bearings too, they are known to come loose on those 470's

 

[Dan Thomas]

That water, as pointed out by 455 Bravo Uniform, is from combustion blowby. In cold weather, you get more of it as it takes a lot longer to get the oil and engine up to temperatures where the clearances close up and the water gets heated and vaporizes and blown out the breather. Doing pattern work in cold weather is not wise, and you end up with that water staying in the crankcase, mixed with the oil, and in the presence of metals to catalyze a chemical reaction, you get nasty acids that eat that engine from the inside. That's where most engine corrosion comes from, NOT from atmospheric humidity, which is tiny in comparison with blowby water vapor.

Cars don't get that anymore. Their clearances are tiny and their temperatures are closely controlled so that blowby is at a minimum. Their oils often contain anti-corrosion stuff that is not compatible with aircraft engine crankcases that contain magnesium. They have Positive Crankcase ventilations systems that draw fresh air though the case the get that water out. The PCV system needs manifold vacuum to work, but in an airplane, where the throttle is mostly open all the time, there is too little vacuum to do any good.

 

[CT583]

That water, as pointed out by 455 Bravo Uniform, is from combustion blowby. In cold weather, you get more of it as it takes a lot longer to get the oil and engine up to temperatures where the clearances close up and the water gets heated and vaporizes and blown out the breather. Doing pattern work in cold weather is not wise, and you end up with that water staying in the crankcase, mixed with the oil, and in the presence of metals to catalyze a chemical reaction, you get nasty acids that eat that engine from the inside. That's where most engine corrosion comes from, NOT from atmospheric humidity, which is tiny in comparison with blowby water vapor.

Well that makes sense. It wasn’t exactly pattern work but was practice approaches and going missed. Somewhat similar.
On cold days, I let the entire engine come up to temp. Waiting on the oil-cooler thermavern to open and oil pressure to decline/stabilize prior to even performing the ground run-up.

If the case held that much moisture, I’m curious if my post flight routine of leaving the oil fill cap off the vent moisture is even relevant in reducing crank humidity.

 

[Dan Thomas]

If the case held that much moisture, I’m curious if my post flight routine of leaving the oil fill cap off the vent moisture is even relevant in reducing crank humidity.

Not much help. The oil and water are emulsified and take a long time to separate. When they eventually do, the water is under the oil in the sump, not exposed to the air. It's heavier than the oil. The thin sheet aluminum sumps used on Continental 470s and 520s have been known to corrode through due to that.

 

[CT583]

Not much help. The oil and water are emulsified and take a long time to separate. When they eventually do, the water is under the oil in the sump, not exposed to the air. It's heavier than the oil. The thin sheet aluminum sumps used on Continental 470s and 520s have been known to corrode through due to that.

I’ll update after my oil change. I’m hoping that since I change oil at 25-30 hours I’m mitigating some of the issues. I haven’t had any reports of corrosion as of yet, but I like to stay ahead of the curve.

 

[I threw it on the ground]

There’s only two oil conditions that should worry you. Very light brown, runny oil, gas is getting past the rings (mostly happens on forced induction aircraft)…. Or shiny sparkly oil……