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Air oil separator for O-540

Flying again!

Flying again!

Well Known Member
I just purchased an RV 10 and it does not have an air oil separator on it. I flew it 9.5 hours cross country last week starting at 9 quarts. I ended at 6 quarts after adding 3 mid way through the flight. The engine has 233 hours on it since being rebuilt by Schmidt Aviation in Florida. It does not appear to be burring oil ( no smoke, no wet exhaust), but it does have oil residue under the belly and cowl. It is not dripping oil, and does have some seeps at the oil returns on some cylinders.

Seems like the first step is to put in an air oil separator. Does anyone have any recommendations? The Super Slime Fighter has an RV 10 specific application. There is also the ANDAIR, M-20 etc.

Thanks, TJ
 
Are you saying that you used 6qts in 9.5 hrs? If so, a separator won't work. You need a top overhaul or some serious cylinder work. You should use a quart in 12-20hrs normally. If you are sure its not all leaking then its coming from your breather big time. In rare cases a bad placement of the breather hose can suck oil like a venturi, but I doubt that's it here.
 
You might check the front engine crank seal first.

I recall reading that a leaky front seal can result in a pressurized crankcase and high losses out the breather. I'd also do a compression check and if low, determine if the leakage is past the rings (airflow out the breather), or past the exhaust valves (airflow out the exhaust). or airflow past the intake valves (airflow out the carb or injection servo).

An air-oil separator would just mask the symptom of a fundamental problem.

Good Luck!
 
I plan to have a compression check and differential pressure check at the same time the DAR checks out the airframe so I can get it rectified in the US. I plan on pulling the cowl soon (hopefully when it gets below 100 deg here!). The mechanic for the first 100 hours says that the breather is routed in the exhaust and may be causing a veturi effect....more to follow.
 
What is he "normal" oil cappacity for your engine? I fly an IO540 that we keep at 6qts. 4 is the minimum for flight. You could be overfilling.
 
540 oil capacity

AN I0540 can have either 8, 12 or 16 quart sumps depending on dash number. Is your engine an I0540-D4A5 that Vans sells?
 
The engine is an IO-540-E4C5. The dipstick is marked to 12 quarts. From what I understand, the min oil level is 2 quarts (!!).

I can't fly for a couple of weeks until I get itninspected by the DAR and get the FAA approval for my application for registration and for the original tail number.

When it is registered, etc., I am thinking of flying locally with the oil level at 6 quarts and to closely monitor it to see if it goes down. The mechanic that did the annual in Jan (204 hours, now 233 hours) did a compression and differential pressure check and everything was ok.

Is it possible for an O-540 to stabilize at 6 quarts? Seems low. Also, should I get the compression and differential pressure check done now before flying again?
 
Mine is no 540 but I do know that if I put any more than 5.75-6 quarts in my 360 all it does is spit it out. I thought I had super high oil consumption till I figured that out. Now at oil change she gets 6 quarts and I keep her between 5 and 6. I get about 15 hours to the quart this way. I have chrome cylinders.
 
1st attack: Fast & cheap, pull your bottom 6 spark plugs and look for oily ones. It wouldn't surprise me if you had one or more that you can pour oil out of. If no oily ones and no carbon blacking & stringing on exhaust tips, you are leaking. If exhaust is coking bad its valve guides or rings. If plug(s) are real oily its rings or maybe guides. Probably ring seat issue. That is, if its not simply been overfilled.
 
My IO-540 D4A has a 12 qt. sump, and I routinely fill it to 7 qts. I get 12-15 hours per qt. and oil temp & pressure are good in all regimes. When the engine was brand new and I was doing first flights, I would fill to 12 qts. in case I had an oil leak or over-temp condition. Just blew a lot of oil over the belly.

Jim Berry
RV-10
 
Differential Pressure Check Done Today

I just did a differential pressure check today. Ran the engine on the ground for a short time to get CHTs up to about 310F and then shut down and pulled the cowling. The pressures were:

#1 75/80
#2 78/80
#3 75/80
#4 74/80
#5 77/80
#6 72/80

All the plugs looked good. There was some minor seeping but no major leaks. Did note that for all cylinders there was a little air coming out of the breather tube. The breather tube is routed far back and about 3 inches above the exhaust pipe on the left side.

At this point is seems that the engine is not burning the oil so it must be pumping it out for some reason.

Next wtep is to put a little Marvel Mystery Oil in the engine and fly for an hour or so (when I get the US regestration...aargh) and then drain the oil and fill to about 7 quarts and monitor closely during local flights to see what is happeing.

Say lots of pros and cons on the install of an air oil seperator, but if I continue to use .5 quarts per hour, and the engine is sound, there are no visable leaks, then theat would be the next step.

Comments?
 
One more thing I'd look for: Pull plugs again. shine a narrow light like a mini maglite in the bottom plug hole pointed towards the piston. Look through the top plug hole while you hand turn the prop. As piston comes toward you about midway you should get a good enough glimpse of the bottom wall of the cylinder and the corner of the piston coming at you. If the piston is pushing a little puddle of oil...you have a new clue. Check all 6. That would be a nice clincher, but I'm afraid you're needing a cylinder inspection regardless, and hopefully just a good hone, well fitted rings and a dose of mineral oil. Once again, that is provided its not an elusive leak after all. I don't like definitively telling someone to tear apart their engine without seeing it. I've seen oil cooler leaks and others that freakin defied discovery.
 
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