Missing Oil Syndrome

What is it?

For those of you who are new (and those of you who didn't pay attention before), Missing Oil Syndrome is the name I gave to a peculiar oil-change phenomenon that many members, including myself, have reported. It works like this: The US version of the SR20DE has an oil capacity of 3-5/8 quarts. Oil changes during the first three or four years of owning my '91 were to spec: I'd drain the oil, replace the filter, and pour in 3-5/8 quarts (or thereabouts) of oil (I have used Mobil 1 or Castrol Syntec) to fill the engine to the proper level. However, over the past few years, it took progressively less and less oil to fill the engine during an oil change -- it's been about 3 quarts for two years now. Hence the mystery; where is that missing 5/8 of a quart. (Incidentally, this strange problem has been rehashed over and over again on the mailing list, so don't go posting inane advice like "Maybe your filter was/is oversized/undersized. Maybe you were parked on a slope. Maybe your dipstick has moved up/down. Maybe you're imagining it. Maybe you're an idiot.) ;-)

Inspiration for a solution

Anyway, after George Roffe reported some buildup and a clogged passage or two upon tearing down a used, well-cared for SR20DE that apparently ran only Mobil 1 its working life, I figured a oil system flush might be worth a try.

A solution

I shopped around several places to find a motor flush that looked semi-reliable, rather than being just kerosene in a fancy bottle. I finally settled on a relatively expensive product from STP for $7.99 (most of the other products were a dollar or two) because the product claimed it reconditioned oil seals and had a few colorful graphs showing how well it cleans different internal areas based on the length of time you run it through the engine. (Marketing guys love consumers like me!)

I ran the STP motor flush through the engine for the maximum recommended time (20 minutes) at a fast idle, between 1500 and 2000 RPM. (STP recommends 1500, but it's nearly impossible to keep an SR20DE at a constant low RPM.) After draining the crankcase and replacing the filter, I added the usual 3 quarts of oil (Mobil 1 this time; it was on sale) and went for a brief drive, parked the car, and let it sit for a few hours. When I checked the oil level again, it was a full half-quart low. Hallelujah!

A bit of reflection

Clearly, there was a sludge or varnish buildup somewhere in the engine that was holding or displacing a half-quart of oil at each change. As further proof of this, I noticed that the freshly added oil was the same light amber color it was as it flowed out of the bottle. During oil changes for the past few years, the oil (whether Syntec or Mobil 1) would immediately darken a few shades on the dipstick - clear evidence that it was mixing with some leftover oil in the engine.

I don't know where the blockage or buildup was, but it's gone now. There are no seal leaks that I can see anywhere in the engine, so my worst fear of using a strong chemical cleaning agent in the engine didn't come to pass. What I would love to know, however, is just where the blockage/buildup was in the engine.

For those of you who've torn down an SR20DE, any ideas?

Conclusion

So, if you're one of the lucky ones whose engine suffers from Missing Oil Syndrome, there may be a cure. Give the STP product a try, and see if you get the same results I did.