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I have a 1991 BMW e34 525i with 374,000 km which burns oil. I don't have any leaks, and I have little smoke when I go uphill and accelerate.

I have replaced the cylinder head gasket set and the piston rings.

What should be next on my list to check or replace?

  • It doesn't smoke? Or it only smokes a little? If so, what is a little? How much oil does it use (1 q/l every xxxx miles)? What other indications are there an issue is occurring? Were the piston rings clocked correctly? Is there any blow-by? At what point does it smoke, when accelerating or decelerating? – Pᴀᴜʟsᴛᴇʀ2 Feb 7 '15 at 21:00
  • it does smoke only when I drive it uphills and do hard accelerating and by a little I meant it doesn't smoke when car is idle or driving it on flat roads. 1.5 litre per 3000 km.I didn't install the piston rings. I don't know about blow-by. – danarj Feb 8 '15 at 8:15
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    In order to rule out the head gasket and piston rings, you should perform a compression test and report back the results. – Zaid Feb 8 '15 at 12:41
  • I'm wondering if either the rings were clocked incorrectly, if the cylinders were not honed correctly, no proper break-in, or a combination of the three. Since it happens when there accellerating, I don't think it's the heads. – Pᴀᴜʟsᴛᴇʀ2 Feb 8 '15 at 13:39
  • I'd start with the basics. Do a compression test and check that the engine is actually healthy after the rebuild. It is possible that the oil you are seeing is something like a blocked breather or failed pressure valve as opposed to related to the engine itself but you won't know that without a compression or leak down test. – Steve Matthews Aug 4 '15 at 10:08
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If the car is still burning oil as you describe, I can think of several things which might be wrong:

  • When replacing the rings, you clocked the rings wrong. If all of the ring gaps line up, you'll pump oil into the cylinder (gives a straight shot for oil to pass). You'll also lose compression.
  • If you didn't hone the cylinders correctly or didn't at least bust the glaze in the cylinders, your rings will not seat, which can provide an avenue for oil.
  • If the rings were not broken in correctly, this could cause ring seat issues as well.

It could also be a combination of any of the three causing the oil burning issues.

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I agree with @Paulster2 that it seems to be related to the piston ring replacement.

Another possibility is that the valve stem seals might be worn, although the symptoms you describe are not quite right, and it would smoke at start-up and long periods of idling (pulling away after sitting at traffic lights, for example). Just my 2 cent's worth. Maybe a silly question, but are there any visible oil leaks under the vehicle or in around the engine bay?

Hope you find the problem.

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  • This would be viable, too, under hard deceleration. I don't think it's the case here, though. As you state, the symptoms don't quite fit what the OP is stating. – Pᴀᴜʟsᴛᴇʀ2 Jul 21 '15 at 15:53

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