Anyone Know What This Maintenance Reminder Is For?

[JCL]

Originally Posted by ard

JCL- figured this would catch your eye...

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....

There have been one or two warnings posted. I think they were all X3 models. No iDrive warning, in that case, but the rest is the same. Not many get the warning because of tendencies to change fluids early and often, over and above manufacturer's recommendations. That's a joke, BTW.

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