Milky Oil... How..?
 

Our Cessna used to get its' oil milky just before service, sometime it did and other times it remained clear oil coloured.
This milkyness is usually caused by water contamination. So can we blame our IMC Pilots for this? , as prolonged cloud flying
is the only way water could have got into the engine.

Explore the possibility that the engine oil is not getting hot enough, long enough to boil off the moisture in the oil. Cover the oil cooler air inlet, and monitor the oil temperature carefully for a long flight (more than an hour). Get the oil nice and hot, but not overheated. If the oil temperature will stabilize at 190F to 205F, and is within the limits for the engine, fly it around for an hour or so that way, it'll help. A short flight, or circuits is not good flying for the engine in those conditions.

The 182RG I used to fly a lot always had milky oil. We tried everything, it was always milky. The plane always ran very well for many years, so we did not worry about it too much...

At this time of year in the UK we often get very high humidity, although it can happen anytime. I wonder if that's a possible cause sometimes? There are more significant reasons why I insist on 50 hour oil and filter changes (even though they're only required at 100 hours) but I'm not a Doctor............

I hope you are joking.
Its not a closed system, the oil breather line is open to outside air.
Every time an engine is shut down as it cools it draws in ambient (humid) air.
Same with daily heating and cooling cycles as the aircraft is parked outside.
Not running the engine long enough or hot enough to boil off the water causes the oil to go milky over time.

My Piper Archer running a Lycoming O-360-A4M suffered the same issue which had nothing to do with the type of flying. I fly both IMC and VMC. As already mentioned it's just down to the ingestion of moisture on the ground and may well be a sign of underutilisation.

I found the remedy was to take the aircraft up to 10,000' in a continuous climb once a month and then do a powered descent over an hour's flight time. I get my oil analysed on every check and the residual water content dropped dramatically after I started doing that. Check your POH but I start leaning back just a little after 5000' with a little reduction from full power to be kind to the engine.

Keep an eye on your oil temperature throughout. The hotter the better but of course staying in the green.

https://cimg4.ibsrv.net/gimg/pprune....3c814e7c7c.png
You may need a winterisatiom kit for your oil cooler to stay in the correct temperature range.
Its basically a metal plate that mounts in front of your oil cooler.

Most of the moisture is not getting in from the outside, it is water from the combustion process. Burning hydrocarbons mainly produces water and CO2 and because of the old design of these engines there is quite a lot of piston "blow by" and the combustion products end up in the crank case. The water then reacts with the some of the other nasty stuff left over from combustion and forms acid in the oil which then corrodes the steel components. A good long run to get the oil hot evaporates this moisture from the oil.

As said above, a short run doesn't get the oil hot enough and just makes the problem worse.

Any blow by would be scorching hot vapor and at pressure go right out the oil breather tube.
That’s what that tube is for.
Oil is being aerated by the crankshaft rshaft counterweights beating it to a froth.
Oil darkens over time because of the combustion byproducts.
Water? No.

As mentioned, water vapor is a by-product of the combustion process and a portion of that blows by the piston rings into the crankcase. However, the only ones you can blame, are those that perform excessive ground runs or only short flights that prevents the engine oil temps from obtaining a value to "remove" that water vapor. And since it is an intermittent issue, if you were to track the max engine oil temps with the current OAT/DWPT by flight or ground run, you can probably narrow down who is the biggest offender. I believe TCM and Lycoming both offer guidance that addresses this topic.

I have also had this occur in the hydraulic oil of an agricultural tractor. We were a bit worried that the water would turn the paper oil filter to mush, which would contaminate the hydraulic system. So we changed all 10 gallons and put in a new filter, also unblocked and cleaned the suction filter.

I don't think any of our members just do ground runs, but I know the IMC lads spend about an hour in cloud ( 100% relative humidity.) When flying VMC, I have never had the T+Ps not in the green.

p.s. B2N2... Water in the oil turns it into something resembling pale chocolate milk-shake. This is not just the dark oil caused by the combustion process..

Yeah, it's not advisable to operate your tractor IMC...

Having the oil temperature "in the green" is, of course, perfectly fine for flying, but may not be ideal for boiling water out of the engine oil. I flew both of my planes yesterday, as neither had moved in a few weeks. My Lycoming O-360 had a cruising oil temperature stabilized at 143F - not enough for my liking. So, in an effort to heat it up (without landing to put on the oil cooler baffle), I hung the plane off the prop at a higher power, with the stall horn bleating, for about 15 minutes. Doing so got the oil temperature up to 157F. Still not hot enough to boil water off, but, a start. It's winter baffle time here in Canada now - today's little job!

Burning aviation fuel produces a surprisingly large amount of water vapour. In fact, the mass coming out of the exhaust is slightly larger than the mass of fuel going in!

As mentioned, its not only having the oil temps in the green but for how long. Lycoming recommends temps at 165 to 200 for one continuous hour which does not include taxi, takeoff, and landing times. TCM states 1 hour flight at normal operation temps. Anything short of that and you leave water vapor in the crankcase. Regardless, in my experience the IMC point is a red herring as if that was true half the piston fleet in the US would have milky oil and they don't.

How in Gods green earth would flying in IMC cause water in the oil?
Cylinder head temperatures are 350-380F with EGT’s in the 1300-1400F range and oil 250-280F.
Mentioning that is either an attempt at a joke or a serious lack of understanding of what’s going on.

I once operated my excavator IMC, although the 'M' was really more 'J' for Jungle .. extremely tall+dense bush on the side of a hill called for a GPS unit in the cab and a track to follow based on known [LiDAR] topography, it worked well :)

No worries with milky oil either, it leaked enough to take care of that :E

FP.

Water gets into the engine through condensation after it cools down after the engine stops running. Check your oil breather pipe for blockage.

Certainly a part of assuring the airplane is fit for flight. Oil breather pipes have been known to ice over in winter flying conditions - exiting moist air freezes at the exit end of the pipe. For many types there is an AD to assure that a hole is drilled up a little in the pipe to provide an alternate "breather" port in the pipe. That said, the breather allows the constant equalization of crankcase air pressure with atmospheric pressure. If it is blocked, a sign of this will likely be oil being forced out the next easiest path by higher than ambient crank case air pressure. The next easiest crankcase pressure exit path is usually the crankshaft nose seal. If you're having that type of leak in flight, you're going to notice!

One of my colleagues has had two engines problems with blocked breathers in C152s, the last one caused a load of black smoke to come into the cockpit.

Sorry old memory isn't what it was, but I think there was a Lycoming SB warning of internal corrosion on low utilisation engines. We once found severe corrosion on an O-360 camshaft about the time of a fatal accident caused by a broken corroded camshaft. I don't think I encountered milky oil in any of our engines despite Ireland's maritime and humid climate, In my ancient Ford it was a blown head gasket ... yet again :*