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swr999 · 2010-02-28, 10:41 AM

Background: I recently finished up a rebuild following a spun rod bearing 'event'. Stock '05 STi. Rebuild included JE skirt-coated pistons, new OEM Sti crank. complete valve job. Car runs fine, has ~2000 mi on the rebuild. I'm using ~1 qt/500 mi on Rotella-T 15W-40. No smoke out the tailpipe or on cold (SoCal) startup. No apparent blowby when removing the oil filler cap. In other words, no clear outward signs of oil usage. The exhaust pipe tip has some black 'dust' deposited on it.

I was (and still am to a degree) wondering about the PCV valve. Thinking that maybe the crankcase might be getting pressurized if the PCV was not working right, I did an experiment. I drilled and tapped the oil filler cap for a hose barb, and connected tubing and a compound pressure gauge. I placed the gauge on the driver's seat where I could see it while driving. Then I drove around. Some WOT, boost, partial boost, downhill coasting. The pressure gauge showed virtually no change in pressure, either positive or negative. In other words, by direct measurement the crankcase is not getting pressurized, no blowby, no boost getting into the crankcase...

So here's another thought. After my rebuild my oil pressure is high-ish. On a SoCal cold startup with the Rotella-T 15W-40 the oil pressure climbs to ~85 PSI at idle, where I assume it is probably hitting the relief valve pressure. After full warmup I get ~82 PSI at 3000 RPM, 25-30 PSI at idle.

Question: Is it possible that at sustained 80+ PSI some oil is getting by the turbo oil seal? Enough to consume the quart in 500 mi? In my reading about PCV, turbo oil seals, oil pressure, and so on it seems this is a possible scenario which could explain my oil usage. I'm considering trying a 'lighter' oil like maybe a 10W-30, and see if this lowers the oil pressure, and if that leads to less oil usage.

I would appreciate any comments and suggestions on resolving this problem. Thanks all!!

2010-02-28, 10:41 AM	#1
swr999 n00b Real Name: Steve Join Date: Jul 2009 Location: San Diego Posts: 14 Car: 2005 Subaru WRX/STi Class: IPtBy If it's worth doing... it's worth doing badly.	An oil usage question Background: I recently finished up a rebuild following a spun rod bearing 'event'. Stock '05 STi. Rebuild included JE skirt-coated pistons, new OEM Sti crank. complete valve job. Car runs fine, has ~2000 mi on the rebuild. I'm using ~1 qt/500 mi on Rotella-T 15W-40. No smoke out the tailpipe or on cold (SoCal) startup. No apparent blowby when removing the oil filler cap. In other words, no clear outward signs of oil usage. The exhaust pipe tip has some black 'dust' deposited on it. I was (and still am to a degree) wondering about the PCV valve. Thinking that maybe the crankcase might be getting pressurized if the PCV was not working right, I did an experiment. I drilled and tapped the oil filler cap for a hose barb, and connected tubing and a compound pressure gauge. I placed the gauge on the driver's seat where I could see it while driving. Then I drove around. Some WOT, boost, partial boost, downhill coasting. The pressure gauge showed virtually no change in pressure, either positive or negative. In other words, by direct measurement the crankcase is not getting pressurized, no blowby, no boost getting into the crankcase... So here's another thought. After my rebuild my oil pressure is high-ish. On a SoCal cold startup with the Rotella-T 15W-40 the oil pressure climbs to ~85 PSI at idle, where I assume it is probably hitting the relief valve pressure. After full warmup I get ~82 PSI at 3000 RPM, 25-30 PSI at idle. Question: Is it possible that at sustained 80+ PSI some oil is getting by the turbo oil seal? Enough to consume the quart in 500 mi? In my reading about PCV, turbo oil seals, oil pressure, and so on it seems this is a possible scenario which could explain my oil usage. I'm considering trying a 'lighter' oil like maybe a 10W-30, and see if this lowers the oil pressure, and if that leads to less oil usage. I would appreciate any comments and suggestions on resolving this problem. Thanks all!!