SonexBuilders.net

hello all,

still learning alot about this sonex with the aerovee i bought a few months ago. mine has an under engine oil cooler, aeroinjector, straight dual exhausts, unrestricted oil breather tube venting underneath: pretty much stock. it was top overhauled 40 hours ago, with the scheduled maintenance done at 10 hours post overhaul by the previous owner and at 25 hours post overhaul by me. it has been dry as a bone in all ways except when the crankcase is full (2.75 qts).

i noticed right off the bat that it tended to blow oil out the breather when i had the crankcase full or near full (2.75 qts) until it got down to about 2.25 qts. it blew next to nothing from that oil level on down. not liking to lose oil, i decided to buy and install an oil-air separator that allows for capturing and recycling the oil back into the engine. it is modeled almost exactly after bryan cotton's efforts, having studied his pictures and followup posts. since this separator install, i have been losing lots of oil every time i fly the plane. in 3 short flights totaling maybe 1 hour, i lost nearly 24 ounces of oil. none came out the breather nor any of the new connections to capture and recycle the oil; all came out somewhere near the front of the cowling, soaked the right and left cowling halves and splattered all over the lower canopy. (i smelled it too...) at first i thought i blew a front seal or the oil pressure sending unit. but multiple, subsequent checks showed no oil from these places. so i disassembled the air-oil separator and removed the round, quarter-sized copper-like restrictor. the air flow was improved but not as free-flowing as the breather had been, which was unrestricted. i also checked the oil cooler lines and all were tight. went flying again and lost more oil from the same places, although not nearly as much. as best as i can tell right now, its the lower half of the engine, perhaps from the pushrod tubes, which are the spring type. i also monitored my MGL enigma for engine oil temperature and pressure during all this time. it has been showing normal pressures at all phases of flight, just slightly higher until the oil temperature warmed.

not having changed anything else except adding the oil-air separator, i am thinking a pressure or back-pressure issue. with the engine setup i have, what might be the first things to leak with high crankcase pressure?

Hi FFG,

No expert however have recalled from my Ly/Con days that most (all?) aircraft piston engines, seem to eject a certain quantity of oil, until the "normal" (1/2- 3/4 capacity ) level is reached.
As a student pilot, I recall being chastised, for filling the oil tank to the full mark on the dipstick, and told not only is is waste of oil, I would have to clean the oil off the belly of the aircraft, deposited there due to my excessive zeal.

It may be simpler to just avoider filling your oil tank above its preferred level.

hi...
i know what you mean. i owned a cherokee 140 (lycoming O320) for many years. it always blew the oil out until it reached about 6 quarts. full capacity is 8 quarts. so i learned to not fill it beyond 6 quarts. right now, the aerovee is just at 2.5 qts, with full being 2.75. i expected it to blow more out the breather until it got down to 2.25 or just under. however, no oil i have lost has come out the breather. it has me concerned that the oil-air separator is causing enough back-pressure to force it out in other places. i am seriously considering removing the separator to see what happens. but still wondering where the most likely place(s) might be for the oil to be coming from under current circumstances.

It seems to me that your oil loss and the fitting of the oil separator might be unrelated, although removing the separator should clear that up. An oil leak as bad as you describe should be pretty easy to trace. I had an oil leak which made hardly any difference on the dip stick but was enough to completely coat the underside of the fuselage. I'd suggest cleaning the engine and then doing a 5 minute ground run without the cowl and it should show up.

Peter

I have no first hand experience as my plane is still under construction but on other forums Ive seen reports where these VWs like to leak out the front crank seal by the prop hub unless you have a little negative pressure in the case.

Also Ive seen a few reports of the dipstick not being calibrated correctly resulting in over filling of oil and anything over 2 3/4 quarts is quickly dumped overboard.

That bronze thing is definitely a restriction. I took mine out right away. I did some other mods to try and maximize flow and to get the flow moving down and spiraling around the inside of the can. Not long ago I removed the stainless scrubber pads. They looked fine but seemed to have gunked up a bit and I was leaking oil from the crank exit in the front. You definitely need to eliminate back pressure there.

hey all,
i truly appreciate all the feedback. all good points which keep my thought processes going....
yesterday, after i thoroughly cleaned off the engine for the 3rd time and made my last set of changes for this, i did do a 5 - 10 minute runup without the cowls off. i never went above 2300 RPMs and saw no oil leak at all afterwards. interesting..... so thinking i had this licked, i put it all back together and went once around the pattern. again, i saw oil on the cowl seams and a few drops (much less than before though) on the canopy. now i'm thinking that higher RPMs are a factor, probably due to higher pressures and the oil dipstick calibrations may be off. so i took the cowls off and sure enough, more oil underneath mostly near the front, a few drops at the oil cooler air inlet, a few drops on some of the pushrod tubes, and a light sheen of oil along both lower front sides of the engine case. but nothing behind the prop, on the prop extension or near the oil pressure sender on top. there was no oil whatsoever on the oil separator, its lines or anything near to it, nor any oil the end of the breather tube.

i too am questioning the oil dipstick calibrations and will soon do an oil change, filling it as if to re-calibrate the dipstick. that should help one way or another. right now the dipstick shows about 2.5 qts.

today, i will bypass the oil separator to make the oil breather setup like it was.

i am really hoping no permanent damage was done here.

thanks again all... will keep you posted.

I have installed 3 different oil separators on my 2 Sonex's. From my experience, the leak you are describing is likely coming from the Aerovee prop hub and probably caused by an increase in crankcase pressure from your oil separator installation. Not unusual with some separator installs.

Until I installed the Anti-Splat oil separator and their crankcase vacuum kit,

https://antisplataero.com/product/the-a ... separator/,

https://antisplataero.com/product/crank ... -complete/

that is plumbed into the exhaust system, I could not get rid of that front-of-engine leak. The day I installed the Anti-Splat the hub leak stopped completely. Plumbing the separator drain into the exhaust with the kit components causes a venturi effect, sucking air from the crankcase, and reduces crankcase pressure. Remember, reducing crankcase pressure below the pistons is equivalent to increasing the engines compression ratio above the pistons which will slightly increase HP.

I now have the same Anti-Splat separator on my RV7-A. Still working great. Check out Anti-Splats website. They have a good video describing exactly how it works.

Just about any breather restriction will cause oil to come out the prop hub seal as that’s the weak point in the pressure side of the oil system. Make sure your breather has an unobstructed outside air source. Also make sure that source isn’t in a positive air pressure area under the cowling causing air to blow back into the breather when in flight. If it’s not that then I would look closely at the sump plate under the oil cooler. Oil can move in weird and interesting places if dripping there and it’s very difficult to get a reliable drip free seal. The pushrod tubes are also a typical suspect but if they weren’t leaking before it’s unlikely they would suddenly start leaking. Finally, check that the fittings coming out of the oil pump and at the cooler are tight. It’s possible you are getting a small leak there under higher rpm/pressure.

Keith
#554

hey all... long day with the plane...

i removed the separator and re-installed the breather setup much like it was before the issues started. FYI... the breather tube had exited and again exits the lower cowling just past and below the firewall, in what i am told is a low pressure area. i then again cleaned off the entire engine, and did another 5 minute runup. this time i allowed the engine to run up to 2600 RPMs for about a minute and between 2100 and 2500 the rest of the time. with this shortened runup, i found oil only in the area of the right side (cyls 3 and 4), seeming to come from where the cylinders slide into the block which is just above the pushrod tubes. 2 of the 4 tubes actually had drops of oil hanging off them. no oil at all anywhere near the prop, hub, front of the engine or around the oil cooler air intake. i also double-checked the oil cooler lines at all fittings. all very tight and dry after the runup.
the other area of concern was the oil sump plate. mine has a temperature sending drain plug screwed into it. but no oil here either, nor from any of the 6 bolts holding the sump plate on.
unless anyone has additional ideas, i plan to do my next oil change early, remove the baffling and valve covers and check/retorque all through bolts and head bolts according to the aerovee specs.
with the separator at least temporarily removed and the bolt torques reconfirmed, i am really hoping this is the end of this issue.

i also checked the links provided by pappas and like what i saw for the separator and crankcase vacuum unit. so i am wondering... can this antisplat crankcase vacuum unit be used along with other air-oil separators?

..... and now a stupid question: besides the piston ring gaps and the valve guides, how else does a crankcase pressurize to send the oil out the breather?

bryan: the only air restriction left in my removed separator is the aluminum plate with about 15 1/8" holes in it. is that where you are at?