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Old 06-13-2017, 02:11 PM   #1
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Join Date: Nov 2011
Default 745 oil in intercooler pipes

Hi - I'm looking for guidance on how to approach an oil leak from the turbo of my 745.

1990 745 ~240k miles was all stock until ~40k miles ago
Rebuilt 15g (professional ~2 years ago) currently ~16psi - has been run at ~20 at times
NPR intercooler
MSII+850cc Lucas. ipd cam straight up
modified crankcase ventilation - 2x 1/2" hoses running from stock oil seperator to atmospheric vented can. Can has vaccum to intake through one-way valve and 1/2" hose to turbo air filter piping.

After a 150mi drive this weekend, I noticed a burning oil smell under boost although no noticeable oil smoke. I feel like it happened suddenly after a WOT pull up an 1/8th mile hill or so. When i got home, I put my hand over the exhaust and noticed a spatter of oil drops on my hand. I pulled the piping from the intercooler piping and saw sticky dried oil on the inside of the pipe. lost ~1qt fresh oil over 300 miles or so. Checked play on turbo and it is tight - no noticeable in/out that I can discern.

Before checking axial play, I immediately thought blown turbo. Then I did some reading here and learned that excessive blow-by can make a turbo leak.

I've always had crankcase pressure issues on this car which is not surprising given its age and the extra boost. I know the motor is pretty worn out put it still runs good and pulls pretty good.

How should I proceed? I don't just want to slap a new turbo on and have the same problem. Do I need a motor? what is the best way to determine next steps? This car is my daily and I don't have as much time as I used to to putz with it - performance isn't as much a priotority as it used to be. Thanks!
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Old 06-13-2017, 02:40 PM   #2
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Join Date: Jun 2004
Location: Massachusetts, USA

Check if you have lots of blow by, you may need to improve your PCV.



Originally Posted by 740freak View Post
how psi a stock can support?
Originally Posted by speedn_j View Post
I think this might be my chariot if I can jew the price down.

1990 780t Kind of Modded 1994 945t Pegz, Tintz, Hidz.
"Rear Wheel Drive, the way God intended. If a car is being pulled from the front, doesn't that mean it's being towed?"

"Lister, you are a polyp on the anus of society." - A.J. Rimmer

Last edited by Ursan; 06-13-2017 at 03:18 PM..
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Old 06-14-2017, 08:48 AM   #3
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Join Date: Nov 2011

Ok, I have done some more reading - specifically on the blow by part. This thread was helpful:
http://forums.turbobricks.com/showthread.php?t=312245 specifically the comment by Duder
High crankcase pressure? How is your crankcase ventilation system set up, and is it clean & functional? Excessive blow-by from cylinders into crankcase can also force oil past the turbine seal.

Most of the time "blown seals" are not. They are little miniature piston rings and therefore have a gap. They depend on an air pressure differential being positive between the turbine (or compressor) housing and the oil drain cavity (roughly equal to crankcase pressure unless you have a scavenge pump).
My first question is: Assuming it was excessive blowby as described above, will the seals return to normal operation if the blowby is eliminated?

I did a cold/dry compression check and got 130/130/130/137 which didn't seem horrible. I also took a look inside with a scope and saw that the cross hatching looked 'OK' or, was at least present.

I did also notice that the vaccuum line to my catch can was off. I put that back on. I think for now, I'm just going to turn down the boost and clean out the intercooler and see if it continues.

here is my current catch can ala cleamframetrap - not sure how much more I can do:

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