How do the BMW OLMs work?

[dparm]

Modern BMWs have an oil life meter that can measure oil quality, but I don't understand how they do that and what it even means. It's hard to find definitive information on it. It shows the miles until a change and the approximate date.

The reason I ask is because I feel like my M3 is suddenly counting down to an oil change much faster than before. I had M1 0w40 put in back in December (1500 miles ago, almost 3 months to the day) when the OLM was saying about 7500 miles/April 2015 until the next change. In the pat 30 days it has started adjusting the mileage downward very quickly, and now says 4500 miles until the next change, but the date has stayed at April 2015.

My driving habits have not changed lately and my city/highway breakdown is still roughly the same. I actually made a brief 200 mile roadtrip about a week ago, so the car is definitely getting on the highway and burning off any moisture in the crankcase.

Thoughts? Is it possibly calibrated to the factory-fill Edge Professional TWS or something?

 

[tinmanSC]

It doesn't measure the oil directly, just temp, rpm, hours on engine, things like that. It's calibrated for BMW spec LL-01 spec oils. Your driving habits have not changed, but the temps have. I'm not certain if it checks total time since the last change (i.e. it's been 6 months since you changed your oil.) I'd be willing to change my mind if you can find me a part number for a sensor.

 

[dparm]

Originally Posted By: tinmanSC
It doesn't measure the oil, just temp, rpm, hours on engine, things like that. It's calibrated for BMW spec LL-01 spec oils. Your driving habits have not changed, but the temps have.


I have BMW technical documents that state it does check oil quality. I doubt it is calibrated for LL01 since the car was always spec'd for TWS, and was only recently allowed to use LL01 (and in NAM only).

I'm still not certain why it suddenly thinks the M1 0w40 is deteriorating so rapidly.

Here are the exact words:



The oil condition sensor increases the function range of the thermal oil level sensor. The oil condition sensor
measures the following variables:

! Engine oil temperature
! Oil level
! Engine oil quality

The engine management system evaluates these measurements. With the oil condition sensor, the electrical
properties of the engine oil are also determined. These properties alter when the engine oil shows signs of
degradation and ageing.


System functions

The following system functions are described for the oil condition sensor:

! Measuring method
! Electronic oil level control

Measuring method

The oil condition sensor consists of 2 cylindrical condensers. The condensers are mounted above one another. 2
metal tubes are inserted one into the other to serve as electrodes. The engine oil is used as a dielectric medium
between the electrodes.

Note!
Explanation of the terms 'dielectric' and 'permittivity'.

A dielectric is defined as a non-conductive material in an electrical field. The electrical field is split by an insulator.

The permittivity (Latin: permittere = permit, let through) is also referred to as the dielectric conductance. The
permittivity specifies the degree to which materials allow electrical fields to pass. The factor indicates by how
much the voltage at a capacitor drops when a dielectric, non-conducting material is arranged between the
capacitor plates


The temperature sensor is seated on the housing of the oil condition sensor. The housing of the oil condition
sensor contains an electronic evaluation unit. The electronic evaluation unit has self-diagnosis. A fault in the oil condition sensor is entered in the fault memory of the engine management system.

The oil condition sensor sends its measured values to the engine management system:

! Engine oil temperature
! Oil level
! Engine oil quality

The electrical material properties of the engine oil change as the engine oil wears and ages. The changed
electrical properties of the engine oil (dielectrics) cause the capacity of the capacitor to change.
The electronic evaluation unit converts the measured capacity into a digital signal. The digital sensor signal is
sent to the engine management system. The engine management system uses the signal for internal calculations
(e.g. condensate in the engine oil).


Note: condensate in the engine oil.
Condensate that forms in the crankcase due to short distance driving can influence the permittivity. If the water is mixed in the engine oil, it also collects around the oil condition sensor.

 

[kjbock]

Originally Posted By: dparm
Modern BMWs have an oil life meter that can measure oil quality, but I don't understand how they do that and what it even means. It's hard to find definitive information on it. It shows the miles until a change and the approximate date.

The reason I ask is because I feel like my M3 is suddenly counting down to an oil change much faster than before. I had M1 0w40 put in back in December (1500 miles ago, almost 3 months to the day) when the OLM was saying about 7500 miles/April 2015 until the next change. In the pat 30 days it has started adjusting the mileage downward very quickly, and now says 4500 miles until the next change, but the date has stayed at April 2015.

My driving habits have not changed lately and my city/highway breakdown is still roughly the same. I actually made a brief 200 mile roadtrip about a week ago, so the car is definitely getting on the highway and burning off any moisture in the crankcase.

Thoughts? Is it possibly calibrated to the factory-fill Edge Professional TWS or something?


Based on the info I've read about the N52 oil senor, it looks like the oil quality is monitored according to its change in electrical properties. Could be the same sensor they use in all their engines. Not sure how to attach the pdf file to my post.

 

[kjbock]

Originally Posted By: dparm
Originally Posted By: tinmanSC
It doesn't measure the oil, just temp, rpm, hours on engine, things like that. It's calibrated for BMW spec LL-01 spec oils. Your driving habits have not changed, but the temps have.


I have BMW technical documents that state it does check oil quality. I doubt it is calibrated for LL01 since the car was always spec'd for TWS, and was only recently allowed to use LL01 (and in NAM only).

I'm still not certain why it suddenly thinks the M1 0w40 is deteriorating so rapidly.

Here are the exact words:



The oil condition sensor increases the function range of the thermal oil level sensor. The oil condition sensor
measures the following variables:

! Engine oil temperature
! Oil level
! Engine oil quality

The engine management system evaluates these measurements. With the oil condition sensor, the electrical
properties of the engine oil are also determined. These properties alter when the engine oil shows signs of
degradation and ageing.


System functions

The following system functions are described for the oil condition sensor:

! Measuring method
! Electronic oil level control

Measuring method

The oil condition sensor consists of 2 cylindrical condensers. The condensers are mounted above one another. 2
metal tubes are inserted one into the other to serve as electrodes. The engine oil is used as a dielectric medium
between the electrodes.

Note!
Explanation of the terms 'dielectric' and 'permittivity'.

A dielectric is defined as a non-conductive material in an electrical field. The electrical field is split by an insulator.

The permittivity (Latin: permittere = permit, let through) is also referred to as the dielectric conductance. The
permittivity specifies the degree to which materials allow electrical fields to pass. The factor indicates by how
much the voltage at a capacitor drops when a dielectric, non-conducting material is arranged between the
capacitor plates


The temperature sensor is seated on the housing of the oil condition sensor. The housing of the oil condition
sensor contains an electronic evaluation unit. The electronic evaluation unit has self-diagnosis. A fault in the oil condition sensor is entered in the fault memory of the engine management system.

The oil condition sensor sends its measured values to the engine management system:

! Engine oil temperature
! Oil level
! Engine oil quality

The electrical material properties of the engine oil change as the engine oil wears and ages. The changed
electrical properties of the engine oil (dielectrics) cause the capacity of the capacitor to change.
The electronic evaluation unit converts the measured capacity into a digital signal. The digital sensor signal is
sent to the engine management system. The engine management system uses the signal for internal calculations
(e.g. condensate in the engine oil).


Note: condensate in the engine oil.
Condensate that forms in the crankcase due to short distance driving can influence the permittivity. If the water is mixed in the engine oil, it also collects around the oil condition sensor.


This is the exact same info I have. You can ignore my other post.

 

[Quattro Pete]

Yup, it's based on a dielectric sensor - amount of contamination in the oil will affect the current flow through oil, at a high level.

 

[tinmanSC]

Wow. that's a first. If that's true, I sit corrected. This comes up often on BITOG, as I'm sure you know. This is for your 2011 M3? Hrm. I don't recall any information about BMW sampling the oil directly, but I guess it's not impossible. There are portable oil life testers that use a similar test to what is described above but I wasn't aware of any car using it. That's pretty cool!

 

[dparm]

Originally Posted By: tinmanSC
Wow. that's a first. If that's true, I sit corrected. This comes up often on BITOG, as I'm sure you know. This is for your 2011 M3? Hrm. I don't recall any information about BMW sampling the oil directly, but I guess it's not impossible. There are portable oil life testers that use a similar test to what it described above but I wasn't aware of any car using it. That's pretty cool!



Leave it to the Germans.

Chicago has had some pretty crazy cold in the last few months, though the car sits for long periods without being driven. I'm wondering if I got a lot of moisture build up or something. I have actually been doing a lot of highway driving recently (200 mile round trip just last weekend), but the "miles until change" continues to fall pretty fast. The oil level itself isn't changing though.

 

[Quattro Pete]

Originally Posted By: tinmanSC
Wow. that's a first.

The concept is not new. Mercedes has been installing these dielectric sensors in some of their engines for years...

http://www.machinerylubrication.com/Read/562/oil-change-filter-sensors

Been discussed on BITOG a number of times...

 

[Quattro Pete]

Originally Posted By: dparm
but the "miles until change" continues to fall pretty fast. The oil level itself isn't changing though.

Just keep in mind, the dielectric sensor reading is only one of the parameters that the OLM takes into account. I wouldn't be surprised of time is also a factor, and maybe things like ambient temps, cold starts, etc.

 

[dparm]

Originally Posted By: Quattro Pete
Originally Posted By: dparm
but the "miles until change" continues to fall pretty fast. The oil level itself isn't changing though.

Just keep in mind, the dielectric sensor reading is only one of the parameters that the OLM takes into account. I wouldn't be surprised of time is also a factor, and maybe things like ambient temps, cold starts, etc.



Good point. I suspect it's programmed to think that towards the end of its life, the oil deteriorates very fast. We didn't reset the OLM when I changed it at the "halfway" point back in December. It still thinks the TWS from April 2013/9,000 miles ago is in there.

 

[NMBurb02]

Are you using the same make/model of oil filter as in the past? Perhaps poorer filtration and therefore higher particulate contamination is being picked up by the sensor?

 

[dparm]

Originally Posted By: NMBurb02
Are you using the same make/model of oil filter as in the past? Perhaps poorer filtration and therefore higher particulate contamination is being picked up by the sensor?


Yes, when I put the M1 0w40 in, I used the exact same Mahle (OEM) filter.

 

[JHZR2]

I was under the impression it looked at the thermal-electrical behavior of the oil. IOW, it is doing a measurement as the oil heats to ID the characteristics of it.

The level reading is somehow related as well, as it takes a while before you can get the level to verify as OK when the car is cold.

My 91 has an OLM that is essentially an injector pulse/time/temperature algorithm, as I understand it.

 

[JHZR2]

Originally Posted By: dparm
Originally Posted By: Quattro Pete
Originally Posted By: dparm
but the "miles until change" continues to fall pretty fast. The oil level itself isn't changing though.

Just keep in mind, the dielectric sensor reading is only one of the parameters that the OLM takes into account. I wouldn't be surprised of time is also a factor, and maybe things like ambient temps, cold starts, etc.



Good point. I suspect it's programmed to think that towards the end of its life, the oil deteriorates very fast. We didn't reset the OLM when I changed it at the "halfway" point back in December. It still thinks the TWS from April 2013/9,000 miles ago is in there.


Ever do acid-base titrations in high school chemistry? Remember what happened when you were almost to the point of the indicator changing?

The rate of buffering slows down substantially. Id imagine that as the algorithm sees you nearing the "equivalence point" it degrades the oil faster so youre not stuck in an acidic situation.

 

[BMWTurboDzl]

While they do use the sensor I would argue that there a Min-Max in terms of miles or some other parameter. But dparm the OLM will drop like a rock sometimes. Especially when you get near the end. All of mine were like that.