TOPIC: Making an oil separator/catch can reservoir combination

In some vehicle applications, it's useful to remove oil and water condensates from crankcase gas flow. The aftermarket and OEM manufacturers recognize this. Today there is a huge array of air-oil separators (AOS) and oil catch cans available. A search on the net or youtube reveals lots of products, and DIY ideas. Some product offerings range in price up to several hundred dollars!

I've posted here in the forum and spoken at length about this topic. Since we Gadgetmen are DIY types, we will look for a way to deal with and make or combine things to serve a purpose. I made a combination of an AOS originally made for BMW cars with a simple home-made catch-can or "drain bottle" to contain oil and water condensates. This combo worked well, but the original drain bottle is too small.

The black plastic BMW AOS is a "cyclone separator" that uses it's shape to give a spin to incoming crankcase gas. This cyclonic spin makes the heavier vapors/liquids condense on the inner wall, and run out the bottom drain nipple. As originally installed on various BMW engines, the bottom nipple has a hose that runs to the oil dipstick tube, or the oil pan. I put a 5/16" I.D. piece of gas hose on it and put the drain bottle on the other end. I decided I wanted a bigger drain bottle to extend the drain interval.

The combination of the BMW separator and catch can reservoir does the job well. I don't need anything pretty, just something that works, and isn't expensive. I just found an ebay auction for the BMW oil separator, for under ten bucks, shipped. Look on ebay for "BMW air oil separator" and you can find it in the results. BMW has used several different types of these, most are very involved designs with a diaphragm and very specific applications. But this simple one is cheap and adaptable. Nothing to replace/wear out, just empty the catch bottle at oil changes. I also don't bother to make a fancy sight tube on the ABS plastic bottle. Mine lives in a place where it's hard to see. No drain cock either, just unscrew the top and dump it out!

it's necessary and assumed that the BMW part is installed vertically and the catch can is set or mounted below it, to get condensed oil/water to flow down into the catch can/bottle/reservoir. I'll let the pictures do the talking and the how-to-do it. The new catch bottle is black 2 inch ABS plastic parts from the plumbing isle at home depot. The word trick to know the difference in ABS and PVC plastics is--ABS is All Black Stuff. There are different glues for these plastics too, I had the one for ABS. I re-used the nylon 5/16" hose fitting from my old bottle, and it has pipe threads, so I used the proper pipe thread tap to thread the hole in the new cap. When drilling the hole, I "sneaked up" on the hole size to be able to tap it. Using a hose nipple with the pipe threads makes for a snug fitting, well sealed, one-part hose connection. The 2" ABS pipe came in a 2 foot length, easy to cut w/ a hacksaw.

Tracy G