Oil catch can 4.2 FSI
 

Here is the oil catch can I installed. I used a oil/water separator designed for an air compressor.

​​​​​​I cut the PCV hose in half coming out of the valve cover and fine oil separator. Then extended them with high temperature hoses.

​​​​I attached the catch can with zip ties to the radiator support for now. So far it has caught a few drops of oil after about an hour's worth of driving. Hopefully this will keep the intake valves cleaner.https://cimg1.ibsrv.net/gimg/www.aud...63e8de1f24.jpg
https://cimg2.ibsrv.net/gimg/www.aud...26cd664069.jpg

Do report back on what you “catch” with some miles and hours. I’m particularly interested in the volume of water and related crud. My instinct from Mini experience—with early FSI (DI) and where a fair percentage of catch cans were fit by enthusiasts—is that it is likely the water +oil emulsion combo from cold start that is likely a lot of what gets baked on the valves over time in an FSI set up. Especially where PCV system hasn’t been set up well for it. Hopefully Audi’s fine oil separation (also on my port W12) is a good head start from factory.

I just checked the oil catch can after 700 miles. Commute to work is 30 minutes of highway driving. Its about an ounce of fluid. The darker top half appears and feels like pure oil, very slick and runny like oil. The lighter bottom half is an oil/water mixture that's slick but very thick and pours slowly.

I checked the hose going to the factory fine oil separator along with the factory fine oil separator, and they were both clean and dry. So the oil catch can is doing its job.

I'd highly recommend everyone to install this. It's very easy and cheap. It cost me about $50 in parts. You can buy better oil catch can install kits for a lot more money.https://cimg9.ibsrv.net/gimg/www.aud...8b2fdd4546.jpg2008 4.2 FSI oil catch can contents.

Is it possible to do this on a 4.2 bfm engine?

Bfm has a slightly different setup, but I don't see why you couldn't do this. It would keep your oil a bit cleaner.

ok, but where would I have to install the separator.

There is a breather hose coming off your driver's side valve cover. That's your PCV hose going to your pcv valve. Put the catch can on the hose coming off the valve cover. You will most likely have to buy 3-5 feet of tubing to extend for the new routing.
Someone with a bfm engine will know better on where to put the oil catch can.

I'll take a look this weekend.
I must say it's a good idea to separate the water uit of the oil with a compressor separator. 👍

Are there any particular catch can product recommendations from anyone ?

All I can say is to NOT use heater hose for the connections. Heater hose is not designed to be in contact with oil for extended periods of time.