Audi S4 DIY Oil Catch Can

I recently finished a DIY oil catch can install on the S. An oil catch can is designed to collect the oil from the vapors put out from the crankcase. In the old days, that vapor was vented to the atmosphere. In these greener modern times, the gases are recycled into the intake manifold and burned, or put into the air intake in turbo cars when they're on boost. Some of the oil precipitates out and over time can foul the intercoolers and make the engine burn less cleanly.

The design I used is based on one from here which was put into a turbo Volvo. I didn't include the snazzy clear hose for indicating how full the bottle is because I gave up trying to find clear hose with temperature ratings I wanted. I also didn't include a drain valve because it'd be a bear to reach where I mounted the can. Instead, I'll just periodically check it by taking the top off the can and sucking out oil with a small hose if I need to. While I had the Y-pipe out, I sanded it and painted it to clean it up a bit.

Earlier this year, with about 85K on the car, I put in the AWE intercoolers, along with some other upgrades, and discovered one to two tablespoons worth of oil in the driver side IC hoses and in the IC itself. I started looking at catch can installations to keep the new ICs clean, clean up the Y-pipe, and to help the engine burn cleaner internally.

Here's the bay before the OCC install. Note the bolt in the back I used to secure the OCC. I removed the bolt, drilled a hole in the middle of a large hose clamp, then mounted the clamp with the bolt.



The supplies I picked up included an aluminum camping fuel bottle for the can, an updated PCV "spider hose" from the Audi dealer, a couple stainless steel pot scrubbers from a restaurant supply shop, lengths of oil-resistant PCV hose to match the inner diameter of the pressure limiting valve and the hose section to the intake manifold, plus a couple brass hose barbs, an elbow, t-coupler, and a bunch of hose clamps. I certainly could have done this on the cheap with my old spider hose, but I wanted to take my time putting it together and drive the car while I was doing it, plus I figured it'd be good to start with nice clean new hoses and valves.

In the following picture, I've already removed the section of spider hose that goes to the IM and includes the check valve and capped off the output from the distributor piece. The picture also shows the spider hose barb that goes to the N75 capped, but I later decided to uncap that and hook it up normally to the N75 since the old N75 hose was pretty clean. It appears most oil doesn't precipitate out until later along in the spider hose. The N75 is a solenoid that controls parts of the turbos and apparently you can vent the sensor to the atmosphere, but I'm pretty paranoid so I hooked it back up like it's supposed to be.



I drilled two holes in the bottle. One about midway up for the dirty side, and one near the top for the clean side. I inserted the barbs and secured them with JB Weld, then painted the bottle black with some high-temp clearcoat. I stuffed one of the stainless steel scrubbers into the bottle to act as baffle material between the two barbs. Air flows very well through the scrubbers, and hopefully all that surface area will help the oil precipitate out of the gases into the can.



Getting the old spider hose out was a pain. The rest was easy, but tedious. The lower bottle barb needed to be connected to the output of the spider hose distributor piece that would normally go to the pressure limiting valve on the Y-pipe. The bend was too sharp for the rubber PCV hose causing a kink, so I put in a brass elbow midway. Out from the top barb, the hose leads to the pressure limiting valve on the Y-pipe, with a T-connector and hose heading down to the intake manifold hose with the check valve. After I took this picture, I had to cut a little off the topmost hose segment between the bottle and the T, then had to move the rest of the hose underneath the boost gauge line to get it to line up with the barb on the pressure limiting valve.



A little hose shortening and rearranging plus putting the painted Y-pipe back in and attaching the valve came out like these pics showing the finished product.







I don't know if this setup will help as well as the commercial OCCs, but it was a fun project and at least I'm pretty sure it won't hurt anything. I only have a couple hundred miles on it so far, so I anticipate it'll be a while before I see any results.