03-09-2019, 11:21 AM | #1 |
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Oil coming out of Pre-Cat O2 Sensor
It's not the Valve Cover Gasket. I just replaced it and have done a thorough inspection around the motor with a mirror. It's all clean. I've also watched with a mirror with the motor running to make sure no oil is dripping onto the downpipe or o2 sensor.
Oil is bubbling at the o2 sensor. Any ideas what the problem could be? The car is a stock X3 35ix with 72k miles. Thanks! |
03-09-2019, 12:31 PM | #2 |
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That sounds like a failing turbo. Oil should not make it to the O2 sensor and be able to bubble out like that without serious issues with the turbo seals. I would triple check that it's not something else dripping into that area, the bubbling may make you think it's from the O2 sensor when that may just be a side effect of the oil dripping into a hot area.
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03-09-2019, 07:01 PM | #3 | |
If it feels good do it.
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03-09-2019, 07:12 PM | #4 |
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Excessive oil burnt in combustion chambers = blue tailpipe smoke. Motor has to be burning fair excess amount of oil for visible blue smoke to be seen. This typically occurs with worn piston rings and/or valves.
White smoke at tailpipe = water vapor/steam...cause is coolant in combustion chambers (typical of head gasket breach). Do you have a feel for rate of oil loss? I'd triple check around that VCG, etc. oil at the O2 sensor location seems unlikely to me to be coming with combustion exhaust gases. |
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03-09-2019, 07:48 PM | #5 | |
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The circled area is where oil seems to be starting, and it flows down to right above the 6pt section where it bubbles and flows onto the downpipe. I don't see any oil on that corrugated sleeve and I've held the mirror to see if anything drips on it and I'm not seeing anything. Is it possible for oil to move upward against gravity while the car is stationary? Also, more oil accumulates and burns there when driving rather than at idle. |
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03-09-2019, 08:27 PM | #6 |
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Is that a photo of THE sensor that is/was in your car?
The sensor threads into the exhaust manifold and is sealed with a metal crush type gasket/washer- see in the pic. So the oil is not coming from inside the exhaust manifold- it has to be dripping onto the O2 sensor's housing and/or attached signal wire (part of the signal wire is protected by aluminum sheath- heat shielding) from some other engine component/gasket that has a leak. I'd bet your new VCG is leaking...it's not that rare to have happen. Sometimes it will only leak a drop or two when motor is pushed to accelerate. |
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03-09-2019, 08:40 PM | #7 | |
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03-09-2019, 08:46 PM | #8 |
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Valve covers are quite pricey; I'd only replace if you feel you likely damaged it (they are plastic and can crack) when you removed it last time; it's very rare they crack unless mishandled.
I'd opt to inspect it after removal and if looks good reinstall- do proper surface prep and you can reuse the new gasket, inspect it also. |
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03-09-2019, 09:15 PM | #9 | |
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03-11-2019, 11:32 AM | #11 | |
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I think on these new N5x engines, the valve covers are thinner than the older counterpart on M5x engines. At least this is my take, once I pulled valve covers from N54 & N52 engines, compared to M54 valve covers, or N62. German law forces car manufacturers to use recycled plastics, hence many issues with these cars since the turn of the century. To check for warp, you need a 100% flat surface, then place the pulled valve cover onto it. Valve cover clean, then first go around with a bright flashlight and check on opposite side. If you see light shining through, it's toast. Some times one side could be ok, use gauges if not sure. But usually the warp is big and can be spotted with naked eye. 0.02
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03-29-2021, 09:49 AM | #12 |
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335i oil leak
I had the same problem with oil leak on the converter. I installed a new valve cover and cleaned everything off. (2012 335I ) it did look as if the valve cover was leaking / seeping. gasket was hard and flattened. since then I have had a phantom oil burning smell after a steady cruse. I didn't see any leaks at the cover. but the oxygen sensor is getting damp with oil at the same place you circled in your picture. I cleaned the area at the sensor and took it for a short drive and it was damp just enough to make a ring around the sensor. I was suspecting the turbo as the problem. did you solve your issue?
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03-30-2021, 02:51 PM | #13 | |
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03-30-2021, 07:01 PM | #14 |
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I have seen oil pressure sensors fail and pump oil into the engine harness. This is a long shot but I would unplug the O2 sensor connector and just make sure the connector is clean and has no oil in it.
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02-09-2023, 05:52 PM | #16 | |
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