Air oil separators

[svanarts]

As far as air oil separators go how dows the Slime Fighter compare with it's larger cousins? My RV-4 doesn't have all that much room on the firewall and I'd like to install as small a separator as I can. Any suggestions as to the best small form factor air oil separator?

[aerial]

When I visited Van's in August they had on display at the front desk an air/oil seperator. Not sure on the brand. You might give them a call and check what they recommend. I found the guys really helpful and friendly.

[Joe Blank]

I use the Slime Fighter on my RV-6 and it works great. Just exit the breather tube over one of the exhaust stacks and it does a great job of eliminating an oily belly. I also NEVER fill my engine (AeroSport IO-320-D1A) over 6 quarts, as it self levels at about that point. I only end up then adding about 1 quart in 25 hours.

[Spike]

Interesting, the O-320 in my 172 behaves the exact same way. No matter how much you put into it it blows down to 6 qts and then sits there happy as can be.
 
-- John
 

I use the Slime Fighter on my RV-6 and it works great. Just exit the breather tube over one of the exhaust stacks and it does a great job of eliminating an oily belly. I also NEVER fill my engine (AeroSport IO-320-D1A) over 6 quarts, as it self levels at about that point. I only end up then adding about 1 quart in 25 hours.

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[hngrflyr]

[[color=violet]quote="Joe Blank"]I use the Slime Fighter on my RV-6 and it works great. Just exit the breather tube over one of the exhaust stacks and it does a great job of eliminating an oily belly. I also NEVER fill my engine (AeroSport IO-320-D1A) over 6 quarts, as it self levels at about that point. I only end up then adding about 1 quart in 25 hours. [/quote][/color]

It's interesting how engines differ. Our RV-6 has a 160 hp 0-320. I change the oil and filter every 50 hours. I install 7 quarts then add a quart when it gets down to six. The engine became due for oil change today. I've added 2 quarts in 50 hours. I need an oil separator too. Gettin tired of greasy belly.

Bobby S

[Mahlon]

The reason this happens is that the amount of oil inside the engine actually changes the crankcase pressure by varying the size of the inside of the engine. If you look at the total volume of space inside the engine, by changing the oil level you increase or decrease that volume of space by adding or removing oil. Adding a quart of oil would decrease the volume of space inside the engine by an amount equivalent to the volume of oil added. With a given supply of air pressure inside the engine(blow-by air from the cylinders) and a given outlet hole (breather fitting) varying the size of the inside of the engine, will vary the resultant crankcase air pressure. The higher the crankcase air pressure, the more tendency, we have to push oil vapors out the breather before the oil can separate from those vapors, resulting in the messy belly and oil usage. Once we get to a internal size or internal volume that is compatible with the blow-by and or breather size the internal crankcase pressure drops to a level that will allow the oil to separate from the vapors before being expelled from the engine, and the belly is cleaner and the usage stabilizes. Anything we do that effects this situation can effect the amount of oil we breath out. Restricting the breather outlet will increase the pressure and cause more oil breathing than a less restricted breather. Worn or unseated piston rings will cause more blow-by and the increase in pressure that goes with it, thus it will cause more breathing of oil out of the engine and like we discussed making the inside of the engine smaller will also increase the pressure making the engine breath the oil saturated vapors overboard. Some perfectly good running engines have less blow-by than others or a less restricted breather outlet than others and that is why some want to run two quarts low before they stop pushing the oil out the breather and others want to run only a 1/2 quart low for the same results. Likewise when there is something wrong with the engine that effects this combination we will breath the oil laded vapors out no matter what we do to try and stop it.