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Oil on the belly

jpowell13

Well Known Member
Having just spent a couple of unpleasant hours on my back cleaning oil off the belly of my 6A, I'm ready to install an oil/air separator. What's the best system that works and isn't too complicated to install. John
 
Oil Breather into the exhaust even without a separator works well. I’ve done that on a RV6 and RV10. Like you I was recently peeved with oil on the belly and ordered an AntiSplat separator. Luckily I really investigated the source of the oil before fitting the separator. Turns out most was coming from the head/Tappet oil drain back hoses. I replaced the hose with the clamp on each end, but replaced the hose clamps as well. The screw type clamps, because they are small, tend to leak more, the more they are tightened, the straight area under the screw just simply cannot be tightened to stop leaks. The answer is to fit the compression type clamps that are on most cars now. These clamps are magic because they squeeze evenly around the hose, especially on small diameter hoses, and they really stopped the leaks. Anyway just a suggestion.
 
oil separator plus case vacuum

I have a -7A with an O-360 and installed an oil separator and later, a case vacuum kit, both by Anti-Splat Aero. The vacuum device plumbs the outlet of the separator to one of your exhaust pipes, which puts the case at a negative pressure with respect to outside air. Installing the separator reduced the oil on the belly, and the case vacuum device eliminated it by stopping the small leaks from the case.
 
I have the anti splat oil separator and after 300 hours not a speck of oil on the belly. The exhaust and led residue is hard to clean off.
 
I just installed an ASA oil separator. I've only made a couple of short flights since, but there seems to be reduction in the amount of oil lost out of the breather tube. Will know for sure once I've made a long flight. John
 
The oil vent system on my IO-360 was per the plans ... a crankcase vent tube down to a slant cut tube dumping on the exhaust pipe. Did some adjusting like looping the hose up as high as possible then down to the exit. Always had oil on the tailpipe and it often would drip onto the deck. It was also all over the belly. The system seemed very sensitive to oil level, and it would dump down to about 4 1/2 qts before it let up and stabilized. Not a satisfactory system in my mind.

So I installed a simple catch can with an internal baffle, one that is used to catch vapors from an auto engine to keep the oil out of the EGR valve, a common cause of poor performance on some setups. I added a ball of coarse stainless steel wool to help vapor condensation, and drilled/tapped an oil return fitting in the bottom of the can that is connected to the crankcase sump. It is also mounted as high as possible, with a simple bent plate bracket, maybe a 1/4" below the upper cowl, creating a nice lift to the can before heading down to the exit over the exhaust pipe.

I used 3/4" hydraulic hose for the plumbing (solvent resistant, ask your auto parts shop) and cut a whistle slot down by the exit.

The exhaust pipe is now COMPLETELY dry, it literally looks the same as the other pipe. The belly also has no oil. I can keep the engine oil level at a comfortable 6 qts and oil usage has dropped as well.

Call that a win win for about $40 and some DIY imagination.

Cheers!
 

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works and isn't too complicated to install

Installed an Airflow Systems Super Slime Fighter, very pleased with. Works well in positive Gs.
Probably the easiest to install, but important to respect the install slope of about 15° for it to work as designed.
 
Cleaning oil from the belly is a time honored tradition and I encourage people to enjoy it.
Aviation is all about risk vs reward, what's the risk of a clogged vent system vs not having to clean the belly?
Dump nasty vent by-products back into my sweet engine, no thanks on that one either.
 
Cleaning oil from the belly is a time honored tradition and I encourage people to enjoy it.
Aviation is all about risk vs reward, what's the risk of a clogged vent system vs not having to clean the belly?
Dump nasty vent by-products back into my sweet engine, no thanks on that one either.

Totally agree, and based on what people like Ed Kollin say, you really want that stuff out of your engine case. This was a very good interview.

https://www.youtube.com/watch?v=Ia-zgGr2pKg

Not to hijack the thread, but I was very surprised that he said UL fuel would not solve the problem that would allow us to run fully synthetic. :eek:

Anyway, I just started using camguard. Will let you know in 20 years or so if it works. :D


ABGB4368.jpg
 
I added a ball of coarse stainless steel wool to help vapor condensation....

Nice example of homebuilding at its best.

One minor note. The steel wool assists in consolidating liquid oil in aerosol form...tiny little droplets suspended in the breather outflow. It is not vapor, as oil has a very low vapor pressure. The last thing you want is condensation, as that would mean condensing water and acids, substances with high vapor pressure, which are in vapor phase if the outflow is kept warm enough. We want them to stay in vapor phase all the way to the system exit.
 
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Some have been known to run an oil breather back to the tail. If you get oil on the belly then you have an engine oil leak. I don't recommend it though.
 
Dan, as usual your keen eye caught my incorrect wording while trying to explain what's going on! I actually appreciate that feedback!

I've noticed that the condenser gets plenty warm, as you can put your hand on it after a flight, and that should keep the water/volatile vapor flowing through the system and out the tailpipe.

Regarding the comments about sludge going back into the engine, the "sludge" people talk about does not exist inside my separator. The wool is oily with no trace of a water/oil emulsion, and the bottom of the collector is coated with clean oil. I am convinced that nothing but oil is returning to the engine.

And thanks for the "Nice example of homebuilding at its best." compliment. I appreciate that too.

Cheers!
 
I must be the oddball - i have the 1/2 Raven and still get oil on the belly, no aero, just straight and level.

Bill, try getting the breather hose further into the wind stream and cut it at a 45 degree angle with the open side facing aft.
 
Oil on belly

I have a full Raven and tapped the breather line directly into one of the pipes
Minimal belly oil even after negative g.
 
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Totally agree, and based on what people like Ed Kollin say, you really want that stuff out of your engine case.

https://www.youtube.com/watch?v=Ia-zgGr2pKg

Not just Ed. But where did he say anything bad about separators?

A good separator system at operating temperature only returns substances with low vapor pressures, oil being foremost. All substances in the return flow are already in the oil, in the same percentage as in the sump, because they did not vaporize. The only way to get them out of the engine is to remove the oil...an oil change.

If the separator system temperature is held at or near the temperature measured at the case outlet (i.e. in the case), it condenses none of the high vapor pressure substances. They continue out the exit in vapor phase.

The vapor pressure of motor oil is roughly 10Pa at 20C. Water is about 2400 Pa.
 
Having just spent a couple of unpleasant hours on my back cleaning oil off the belly of my 6A, I'm ready to install an oil/air separator. What's the best system that works and isn't too complicated to install. John

I like a little oil on my belly because I know it's alive and breathing. try the wash wax for grease. spray it on, wait 5 minutes, wipe it off. 10 minute job. I do it twice a year.
 
Not just Ed. But where did he say anything bad about separators?

A good separator system at operating temperature only returns substances with low vapor pressures, oil being foremost. All substances in the return flow are already in the oil, in the same percentage as in the sump, because they did not vaporize. The only way to get them out of the engine is to remove the oil...an oil change.

If the separator system temperature is held at or near the temperature measured at the case outlet (i.e. in the case), it condenses none of the high vapor pressure substances. They continue out the exit in vapor phase.

The vapor pressure of motor oil is roughly 10Pa at 20C. Water is about 2400 Pa.
Apologies, I inadvertently linked my experience so far with my new engine without a separator and the relative ease of cleaning the belly to Ed's comments on what happens with combustion gasses that go into the oil. I was agreeing with Walt - get the nasty byproducts out of the engine. I'm told that this can safely be done with a good separator but I don't have any direct experience. Ed didn't say separators are bad (that I can recall), he spoke about the byproducts of combustion that a good oil package needs to capture and that we need to vent out all the moisture we can, which of course everyone knows.

The part that was surprising to me was that it seems dealing with these combustion gasses and fuel contaminating the oil are the main challenge for our oil.
 
I was agreeing with Walt - get the nasty byproducts out of the engine.

A separator with a sump connection does return substances with high vapor pressure (notably liquid water, fuel and acids) to the engine when the system is cold. When cold, those substances are in liquid phase, and the separator treats them just like the tiny aerosol oil droplets.

So, until temperature comes up, they re-cycle back into the engine. When the engine and separator system reach normal operating temperature, they are ejected in vapor phase, same as an open breather. The short period of cold operation is the only time when a good separator installation returns water to the sump.

Note "good". "Bad" is a separator system running at low temperature, because it acts as a condenser. It is always returning water and other **** to the sump, if it lowers the temperature of the outflow gasses below the dew point of those substances. Keep your separator warm!

When at normal temperature, measured breather outflow at my accessory case port is about 200F, roughly 15 higher than indicated oil temp. Outflow measured in the line connecting separator can to exhaust tap is 170~175F. Note the breather hose to the separator can and the can itself are both insulated so they cannot become a condenser. These temps are well above dew point for those nasty byproducts which can actually be removed by any breather. The nasty things with low vapor pressures, particularly those soluble in oil, cannot be removed except by oil change.
 
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Note "good". "Bad" is a separator system running at low temperature, because it acts as a condenser. It is always returning water and other **** to the sump, if it lowers the temperature of the outflow gasses below the dew point of those substances. Keep your separator warm!

When at normal temperature, measured breather outflow at my accessory case port is about 200F, roughly 15 higher than indicated oil temp. Outflow measured in the line connecting separator can to exhaust tap is 170~175F.

Dan - This 15F delta between the case port and the indicated oil temp - is this a normal temperature spread, or are you getting this spread BECAUSE you have insulated your breather tube?
 
Dan - This 15F delta between the case port and the indicated oil temp - is this a normal temperature spread, or are you getting this spread BECAUSE you have insulated your breather tube?

Measured right at the accessory case port, upstream of the insulated tube. Breather outflow is piston ring blowby, leakage mostly on compression and power strokes, so naturally it's warm.

I only mentioned oil temperature because a lot of folks assume indicated oil temp also describes breather outflow temp. Not so, although an engine with a lot of blowby tends to also show high oil temperature...those hot combustion gasses heating all the flying oil droplets in the crankcase.

I removed the confusing second reference to "15F" in the previous post. Rest of the story...I measured separator can outflow as ballpark 160F, then insulated the can and measured again, then insulated the case-to-can hose (photo below) for a third measurement. Insulation pushed the can outflow up abut 15F, buying additional margin above dew point. Look close in the photo, and you can spot the thermistor stuck in the side of the black can outflow hose.
 

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