Smoking NG900

1142 Views 4 Replies 3 Participants Last post by Shanes96Turbo, Aug 17, 2010

Shanes96Turbo

Discussion Starter · Aug 16, 2010

So, Ive got a '96 NG900, I just changed the turbo with a newly rebuilt unit from Chadwick, My old one had 140k and was putting out alot of smoke.

I immediately noticed an improvement with the new turbo and didn't notice any more smoke from my exhaust. Fast forward to about 1500 miles later...
I've been doing alot of highway driving in and out of traffic.

Sometimes when I slow down to a stop in traffic I notice blue smoke pouring out of my exhaust at idle speed; sometimes its there and sometimes its not. Revving it a little bit will make more pour out but then after moving in traffic for a minute or two it will be gone. I noticed this about 4 or 5 times when I was in stop and go traffic for about 5hrs today. When doing WOT pulls the car pulls nice and I don't notice any smoke during or shortly after when slowing down after the pull....seems the smoke is only occuring when the engine is under vacuum

I've modified the PCV system a bit just to rule that out as a possible cause, I've unhooked the large metal pipe that vents fumes from the valve cover to the turbo intake and attached a temporary small air filter right on the valve cover fitting, I've unhooked the PCV valve from the TB, (Putting a cap over the TB nipple) and just let the small hose dump out under the car. I figure this would eliminate any possible PCV problem that could cause smoke/oil being brought back to the intake?

My only idea is that is it possible my intake/intercooler piping and exhaust (3" DP with Saabsport) has so much oil residue from the old turbo that it is deciding to burn off even 1500miles later?

Any suggestions are appreciated,
Shane

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christian900se

· #2 · Aug 16, 2010

First things first: have you checked the oil level to see if you are still losing oil? I remember when I was still running stock Saab 5w30 oil and I got a lot of oil blow by, so much so that there was pools in the intercooler plumbing. It took a long time for it to go away after I switched to Shell Rotella with zero blow by.

Second: I would not be surprised if you still have oil pooled in the exhaust whether it is in the cat, resonators, or muffler.

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saabkid37

· #3 · Aug 16, 2010

did you figure out why the other turbo died?

typically, when a new turbo is installed you either need new oil lines, or to do a very thorough cleaning of the lines, as coking in the lines may have caused the first death, and now has caused a quick second.

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Shanes96Turbo

Discussion Starter · #4 · Aug 16, 2010

Just checked the oil level and its at about 7/8 (just before the full mark) so I couldn't be loosing that much, when I did an oil change 1500miles ago I put in the recommended 4.2quarts.

I believe I put in 5W30 Mobil 5000 conventional oil, I've been weary of switching to synthetic because I'm afraid it will cause unwanted leaks and might stir up any sludge clinging to the walls of my engine. I do always change the oil every 3months/3000 miles though.

When I pulled the old turbo out, I did blow out all the old lines (which were unblocked) before reinstalling them. I attribute the death of the old turbo just to be from normal wear and tear (it had 140k on it) When I bought the car at 110k my friends always said there was a trail of smoke behind me when I got on the gas (and that was 4 years ago). But I didn't notice it, and it didn't seem to consume any noticeable amount of oil, until just recently when it started smoking a bit almost all the time when the car was running - thats when I figured it was definitely replacement time.

Christian, what weight of Shell Rotella were you using?

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Shanes96Turbo

Discussion Starter · #5 · Aug 17, 2010

After some more investigation my friend and I have determined the problem not to be the turbo, but to be excessive blow-by. It appears that there is a good amount of crankcase pressure building, more than normal. Playing with the PCV system hooked up and not hooked up yields varying amounts of smoke...

Today the smoke has gotten worse to the point where the car can't be driven because under vacuum there is so much thick blue smoke pouring out the exhaust almost all the time.

Compression is 180ish on all 4 cylinders so we're leaning towards valve seals. Anyone have any insight on this?

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