I'm not the first person to have thought of this project. I've come across a number of sites on the web with instructions for making your own oil catch can. You can also buy nice already-made examples. I think this is slightly more satisfying and cheaper. So far, I've only installed one of these on my 245, so that's what is illustrated in this article, but the principles apply to any turbocharged vehicle. I am not a mechanic, and I disclaim any liability for anything you do to your car.
The rotating crankshaft churns up a lot of oil inside the crankcase. That vaporized oil fills the crankcase, which is pressurized by the movement of the pistons. If there were no ventilation, the pressured oil vapors would be forced past the piston rings ("blow-by") and burn in the combustion chamber. This would create a lot of smoke in the exhaust (often a sign of a clogged PCV (positive crankcase ventilation) system). To prevent this positive pressure from creating blow-by, the block has a vent. This vent takes the form of a hose leading to a box on the side of the block. The box has a hose that leads to the intake. Because the intake creates a vacuum, the pressure in the crankcase is drawn out through the box on the side of block. There are baffles in the box that are designed to trap the vaporized oil and allow it to drip back into the crankcase. Not all of this vaporized oil is effectively trapped. This leads to vaporized oil being sucked into the intake. The oil will collect in the intake plumbing, including the intercooler. Some of the oil makes its way into the cylinders. This, too, can create smoke, but more importantly, will decrease the effective octane rating of the fuel being injected. The solution is to add another separate set of baffles before the intake tract in order to remove more vaporized oil. An oil catch can does this. A catch can is located on the hose between the original PCV box and the intake plumbing.
These are the things you'll need to build your own oil catch can.
An oil catch can only needs two nipples, one for the incoming hose and one for the outgoing hose. So long as these are at a right angle to each other, the vaporized oil will tend to precipitate out in the can. Stainless steel wool can be used as a baffle, but is not necessary. Only use stainless wool, as you do not want wool that will rust! To make a better catch can, it's helpful to have a lid, so that the inside can be occasionally examined. A drain tube in the bottom of the can makes it easier to empty. (A catch can does not recirculate oil, and must be periodically emptied.) Finally, it helps to be able to see the level of oil accumulated without opening the can. A clear hose will serve as an oil level gauge.
1. It may be helpful to place the catch can where you plan to install it in the car, and take some measurements to make sure your hoses will be routed in a sensible way. Once you are happy with the placement of your hose nipples, drill holes in the can to accept the threaded nipples. See the picture below for my placement of the hose nipples. The two 5/8" nipples are located at right angles to each other to encourage oil precipitation inside the can. The drain valve is located in the bottom of the can. The oil level gauge assembly needs to have its lower nipple located as low as possible for best readings. Be aware that the threads on these parts will not likely hold them in place securely, unless you've sized your holes just right. That's okay: we're going to JB Weld them in place later.
2. Now is a good time for a test fit in the car. Figure out how much hose you're going to need to plumb the catch can.
3. With this particular placement, there may be difficulty with accessing the drain valve. Make sure it will clear the intercooler in both positions.
4. Once you're happy with how everything will fit, mix up the JB Weld and apply it to the hose barbs. This will keep everything sealed up properly. It may not be as pretty now, but function must come before form! I've never tried painting JB Weld, but it could probably be prettied up a bit.
5. Let the JB Weld cure for the entire suggested time. No point in rushing things. Once it's done, install the catch can in the car. I used two zip ties to hold it securely in place. Run one length of hose from the PCV under the intake manifold to the catch can. Run another hose to the hole in the intake plumbing. Be sure the drain valve is closed, and, to make draining easier, run a hose to the underside of the bumper. Clamp everything securely with hose clamps.
6. That's it! This is a simple modification, but will keep your intake plumbing much cleaner. Don't forget to periodically check the catch can to see how full it is. Any oil you empty from it will need to be replaced in the crankcase, although it doesn't need to be done every time. Just keep an eye on your dipstick! (Of course, you're not losing any more oil than before--you're just capturing it before it gets into your intercooler and intake.)
