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#21
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I dont think we know really WHAT is being measured by the BMW capactive 'oil quality' sensor. Metal? Viscosity? A combination? I will bet money that it cannot, however, measure 'additive package'. but thats not the topic here. The odd thing is that I cannot recall ANYONE posting a CBS warning to change transfer case oil, ever.... |
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#22
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Last edited by ZetaTre; 12-18-2014 at 02:27 AM. |
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#24
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Off topic slightly
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I think we do know what the engine oil sensor is measuring. I think the technical papers from the sensor developer were posted, and I recall an SAE paper. I remember reading them years back. Capacitance, in combination with the integrated fluid temperature measurement in the sensor, correlates to degradation of the oil. They are measuring oxidation directly, soot in some cases, water in some cases, and additive depletion (the technical phrase used by several different manufacturers of these sensors). I would suggest that the additive depletion is related to TBN, or alkalinity. That would be an indirect measure of additive depletion. As additives are depleted, the TBN drops from the starting point. The computer is calculating the relative drop, and using a map to check if it is in the expected range. If you go to a good oil sampling lab, they will use starting TBN and measured TBN to evaluate oil condition and report on the need to change it, instead of focusing on the trace elements which are commonly referenced, and which refer to engine wear rates instead of oil condition. You can't measure contaminants without things like mass spectrometers. One sensor manufacturer refers to contaminants, but I think they mean glycol or water. Maybe soot. Particle counters are available, but not rugged enough for mobile applications IMO. And I don't know of anyone using a similar sensor for viscosity measurements. Edit: my research was a few years back. The link provided in the post above is BMW info but relates to the Continental sensor. I did have the Continental tech paper at some point, and it discussed additive depletion. I went to find the Continental sensor paper as a link, and found this following summary. It seems there are viscosity sensors now. And additive depletion is mentioned as a correlated output from a system using a di-electric capacitance sensor, which is the technology Continental supplies to BMW. Another sensor is listed as monitoring additive condition by relating dispersed soot to undispersed soot, a function of the soot dispersion additives and how many of them are left. Ard, you owe me a beer some day. Determining Proper Oil and Filter Change Intervals: Can Onboard Automotive Sensors Help? Jeff
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2007 X3 3.0si, 6 MT, Premium, White Retired: 2008 535i, 6 MT, M Sport, Premium, Space Grey 2003 X5 3.0 Steptronic, Premium, Titanium Silver 2002 325xi 5 MT, Steel Grey 2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue Last edited by JCL; 12-18-2014 at 03:02 AM. |
#25
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Just a quick update but first i want to say thank you for being so informative. I appreciate relying on my brothers on the forum for help.
I went to an indy BMW Specialist earlier today. Without mentioning what I heard previously from the BMW Service Center, the mechanic checked the CBS and quickly confirmed, the oil needed to be changed in the transfer case. He mentioned its a routine maintenance. The vehicle generally alerts the driver when its time to change the oil. He quoted be $80 labor plus the oil. |
#26
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We are in general agreement...
My point is that there is a bunch of hand waving going on with many of these lay press pieces, as well as 'trust us, we are omnipotent' from the mfg... and my specific point with quoting JCL was that none of the sensors measre "depletion of the additive package". Note that I am not saying the capacitance they measure and the ways in which they filter and reduce these measurements are useless, nor am I saying they do not correlate with oil life. They most likely do. We just do know know the correlations or errors or foibles. We have water, soot and fuel contamination...as well as changes in viscosity...and changing wear metals... does the sensor measure one of these? some of these? or is it simply a correlation wherein multiple aspects combine in non-linear ways, but by testing a correlation has been developed to allow that to say "this oil is probably bad"? From continental: Quote:
I suppose that somewhere, behind a large NDA, you can find UOAs with correlated long term sensor readings- curves, frequency spectra, etc, etc... But we dont have it here. We meet up, Im buying beers for both of you. |
#27
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While we are at it- same article, different sensor:
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Sounds a bit different than the BMW.continental sensor. Say, I wonder if there IS some method to BMWs madness that ONLY BMW oil be used...so the sensor has a known baseline? |
#28
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Back to the original topic, this is also why it would be important to reset the adaptations when changing the transfer case fluid, even if the flag hasn't been tripped for oil degradation. While the sensing technology is different, it seems reasonable to me to let the system function as designed.
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2007 X3 3.0si, 6 MT, Premium, White Retired: 2008 535i, 6 MT, M Sport, Premium, Space Grey 2003 X5 3.0 Steptronic, Premium, Titanium Silver 2002 325xi 5 MT, Steel Grey 2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue |
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