After my car runs for awhile, it starts intermittently blowing smoke out of the exhaust, and from under the hood (near the turbo, but it's difficult to tell exactly where it's coming from). Problem disappears at speed (>40MPH or so), and doesn't really start until the car is warmed up.

I'm on my second engine. I had the turbo professionally rebuilt when the engine was out. In the current configuration, the oil drain tee's. One side of the tee goes to the oil pan drain plug (-10AN bung fitting in place of drain plug), the other goes to the front of the engine, but that outlet is slightly higher than the oil drain on the turbo.

I realize this isn't ideal and I'm looking at ways to route things so that gravity can actually do its job, but would a backup in the return lines cause oil smoke both from the turbo and through the exhaust?

Car runs fine - just obnoxious and embarrassing.

(Yet again on the 06 Solstice, 2.4L with aftermarket turbo. )

It's worth noting that this particular problem is why I (most recently) replaced the engine (cheaper than rebuilding). I'm getting the feeling that was not necessary.

I'm considering getting rid of the tee configuration and just going with a single line from the turbo to the oil pan, and installing a check valve in the line. I am not sure if this is a good or effective plan.

  • I'm just wondering why you have it tee'd in the first place. You should only require a single return as long as it's big enough. I believe you want the return line to be bigger than the pressure side so it will drain cleanly. If there is back pressure, I would think it could be forced out by the bearing and cause exhaust smoke. Considering you just had the turbo rebuilt, I'm doubting this could happen, though. I'd think the seals should be keeping it in. Keeping this as a comment because I'm unsure of all this. Oct 4, 2015 at 1:11
  • @Paulster2 the turbo kit came with the tee, I was just following instructions. :) my understand was that since the oil coming out of the turbo can me foamy (??) having an additional line effectively increases bandwidth to compensate for lower density. I'm just guessing.
    – 3Dave
    Oct 4, 2015 at 1:54
  • @Paulster2 you clearly know more about this car at this point than I do. How about I send it to you to fix? 😃
    – 3Dave
    Oct 4, 2015 at 1:56
  • Haha - I wish I could! Sounds like an interesting car to work on, lol. I also thought the drain was supposed to be lower than the turbo outlet for the same reason. Oct 4, 2015 at 2:53
  • @Paulster2 yeah. so I thought draining into the pan would be fine. However, the drain plug is on the bottom of the side of the pan. Oil foam coming down the line into the pan would be fighting liquid oil to get into the pan, which (it seems to me) would cause backup in the return line. I'd rather not have to drop the pan to weld in a bung at a higher point. That may be why the kit has two output paths.
    – 3Dave
    Oct 4, 2015 at 5:01

1 Answer 1


So, the oil return lines I had were braided stainless steel, 5/8" ID, -10 AN fittings to the oil pan and timing cover.

Unfortunately, the lines were too long, and the one going to the timing cover wound up shaped like a P-trap. This apparently prevented the frothy oil coming out of the turbo from flowing through the line, causing backup into the turbo.

Turbos have seals that are more like piston rings than gaskets. They're made of metal, circular and have a small cut to allow them to expand and contract (and makes it possible to install them). When oil pressure inside the turbo gets too high - say, if your stupid return lines aren't working - you get blow-by, and the oil exits through the exhaust, resulting in large clouds of oil smoke.

The smoke I saw from the turbo appears to have been coming from improperly-installed heat wrap on the exhaust manifold.

I removed the heat wrap and made some lines of the correct length. It's now day 3, and I've seen no smoke so far.

Fingers crossed!


Yeah, that hose configuration didn't work, either. When I recently rebuilt the engine, I tapped the block just above the oil pan and below the turbo, and ran a SS line from the turbo outlet. No issues in about 5000 miles.

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