Hello:
The oil separator box is located on the block just below your flame trap housing-- they are connected by a short rubber tube. This box is black plastic and contains baffles that allow the oil fumes to condense and run back down into the pan or to be carried up to the air intake to be burned if they are in airborne form.
The simple blow-through test is a very crude measure of the breathing ability of the box. I have had cars with oil leaks that "passed" this test. Basically, if your flame trap and the associated upper plumbing are clear, then the most likely cause of your oil leaks is partial blockage causing elevated crankcase pressures, with the oil following the path of least resistance and leaking from seals or the filler cap.
You can remove the box without pulling the intake manifold-- remove the IAC valve and its hoses for more access, and use extensions and a universal between the intake runners to get to the 12mm bolts. You will need an 0-ring that seals the box to crankcase. The wiring harness in the vicinity may be held to the top of the box with a small bolt as well (8 or 10mm).
Once you have it off, use screwdrivers and picks to scrape out as much crud as you can. Then tap it vigorously and shake to loosen more debris. Once you get the big stuff out, soak it with carb cleaner, block the ports and shake it. I ran hot water through mine and tapped the sides at the same time, which resulted in much more debris coming out.
My 200K mi+ 945 "passed" the blow-through test, but was leaking a small amount from the rear main and front seals. I cleaned the oil separator and put things back together-- no more drips in the driveway. Your results may vary, but it is worth a couple hours in my mind.
Some here have advocated simply replacing the oil separator box-- that is an option you could consider too. Cleaning it takes patience, and because of the baffling inside, you never really know how clean you have gotten it.
Good luck!
--
Herb Goltz, Aurora, Ontario, Canada '92 245 w/130K mi, '92 945T w/200K mi
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