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I'm at 50 hours with my Aerovee and I don't return the blow by oil to the engine. I catch it in a seperator and dump it. The volume, per hour, gives me an indication of how the rings are breaking in, and my Cessna guru says it's a bad practice to return it because it's contaminated. But, managing the oil level, with that dip stick, is not easy.
My question is: Do you think the top oil cooler drains, when the plane is sitting, and gives a false indication of more on the dip stick? I haven't done the before and after running checks yet. Just asking.

I'd like to better understand this also. I check my dipstick before and after flights. Before, the level is higher than afterwards, but I don't know if it's due to the oil cooler draining or that the cold oil sticks to the dipstick differently.

I'm also curious if those of us with the top oil cooler are supposed to run a higher oil level.

Sonex says 2.5-2.75 quarts is common. I've been adding oil when my pressure starts to fluctuate since that seems to happen before I can tell with my dipstick markings. Usually it seems to stabilize within a few psi, but when I notice it bouncing around I add oil. Based on this, I feel like 2.5 would be too low for my engine and have been trying 2.75-3 quarts. I've also had an oil leak and might be losing oil faster than I should (wasn't as obvious during the frequent oil changes at first).

Let's see, there are 2.5 qts of oil that stay in the engine and that's OK....but the few ounces that end up in the separator are "contaminated"?

One solution you may consider (if you already have the oil separator) is to add the new oil sump/filter assy that AeroConversions offers, and run the drain line from the separator back to the sump. I've lost '0' zero oil since this installation, even during aerobatics.

I’ve been flying a Cessna 150 for 20 years and still own 1/3 of it. The Cessna guru preaches that you should not return blow by oil to the crankcase because it is contaminated with NO2 and if you have a filter and don’t change oil every 25 hours it does bad things to your camshaft. I have followed this advice through one O-200 overhaul and I believe it’s true. The cost is a little oil. With oil analysis, I ran that engine 400 hours over TBO and when it was torn down, due to guilt, there was nothing wrong with it. I saw the separator on the internet some where for a couple of hundred dollars. I made mine out of a pint Ball Jar which is suspended by a hose clamp around the screw on lid. The jar is calibrated in ounces so I can measure the amount that is blown out which indicates the break in of the rings. A wad of stainless steel scrubber wired to the bottom of the lid helps the oil to separate and stay in the jar. So far, 45 hours, there is very little that does not stay in the jar. It’s mounted low on the firewall so some gets on the belly. Lets face it, airplane bellies will never be clean.

I too have a hard time reading the dip stick. The drag out oil from the tube confuses the level. In fact I made a new dip stick from 1/8 copper tubing, same size, same style, flatened it out and sweged it on the cable, but I drilled small holes at four levels. This helped a little. If the is oil in a hole that's the level. I also have had oil presure fluxuations. I don't like that because that means the oil is getting below the pick up tube. The temp doesn't indicate a problem when it does that but, it's not a good idea to let it get that low.

With the Aerovee, you need to change your oil every 25 hours. Sonex recommends the oil return line inspite of what the Cessna guru preaches. I concur with Sonex on the oil return line. Depending on the flight conditions, your engine can put a 1/4 of a quart of oil into the oil separator in just a few short hours. That is a significant amount of oil when your engine only holds 2 1/2 quarts of oil. It is tedious to have to remove your cowling just to put a quarter quart of oil back into the crankcase, especially if you are on a long cross country. I went for 50 hours without the oil return line and keeping the oil at the correct level was a challenge. Also, with the Aerovee, you have a TBO of under 1000 hours on average, so it may not be as critical as for an engine with a 2000 hour TBO. I say follow Sonex's recommendations and you will have many fewer headaches.

Jake