PDA

View Full Version : Interesting 'Oil Life' calculation method by BMW


DSXMachina
03-23-2010, 12:28 PM
There's been a lot of discussion in the past about how often we should change our oil. We've also talked about how BMW has an official 15,000 mile interval, or one year, whichever comes first policy.

I stumbled on this BMW document today which sheds some interesting light on the subject. Note a couple things. First is how they say they have recommended an annual interval "in the USA". Hmmm, what is it elsewhere?

More interesting though is how the ECU calculates recommended oil change intervals. It isn't done based on time. It isn't done based on mileage! It's done based on your MPG which is an indicator of how hard you push your car. The easier on your car you are the greater your MPG, the harder you push it the lower your MPG.

The most interesting thing of all is that BMW therefore, by virtue of your MPG, can determine how you drive your car. This data must be stored in the ECU memory somewhere.

Below is quoted a BMW technical service bulletin. Bold print was added by me for emphasis.



July 2008
Technical Service

This Service Information bulletin supersedes SI B12 25 05 dated December 2005.

[New] designates changes to this revision

SUBJECT
Engine Oil Service with CBS4

MODEL
[NEW]

E70, E71, E82, E88, E90, E91, E92, and E93 with the N51, N52, N52K, N54, N62TU, and N63 engines

[NEW] INFORMATION
With the introduction of the E90 also came the next generation of Condition Based Service CBS4.

The primary change from previous CBS strategies is that the oil service forecast distance remaining is calculated and displayed separately from the time-based or absolute service-due date.
The mileage interval forecast calculation by the DME is primarily based upon an actual fuel consumption variable, which reflects the current driving profile.

It is the total fuel consumption, and not the accumulated mileage, which influences when the next oil service will be forecast as due.

The displayed mileage until due is only a forecast, and begins to decrease at a quicker rate once the remaining percentage drops below 50%.

If the actual fuel consumption profile increases or decreases from baseline averages, the mileage interval forecast will effectively increase or decrease as well.

The learned driver profile (average fuel consumption) is also used to calculate the next forecast mileage after a CBS reset. For this reason, a starting point of up to 30,000 km (19,000 miles) may be expected for a vehicle achieving lower than average fuel consumption.

The oil service will also be forecast as due 24 months after the last CBS reset, and will prompt for the service if the forecast based upon fuel consumption has not been reached.

However, it is recommended in the US market to change the engine oil at least once a year. More details concerning the low mileage annual oil service may be found in SI B00 04 01.

The CBS intervals for other maintenance parts, such as the microfilter and spark plugs, are now linked directly to a multiple of the oil service. For this reason, it is important that the oil service counter be set to indicate the correct service currently being forecast.

The SBT 000104070 (Condition Based Service), SBT 000406148 (Modifications to Condition Based Service, and SBT 000206146 (CBS - E70/71) all contain additional information on Condition Based Service strategy and functionality.

WARRANTY
Information only

furby076
03-23-2010, 12:35 PM
http://brightminds.files.wordpress.com/2007/08/big_brother_is_watching_you_red.jpg

cwinter
03-23-2010, 12:36 PM
(snip)

The oil service will also be forecast as due 24 months after the last CBS reset, and will prompt for the service if the forecast based upon fuel consumption has not been reached.



Interesting info, DSX, thanks for posting this.

The above line makes me wonder if I was just not looking right at my date indicator for the oil change. I could SWEAR it used to say 3/2010 but now says 3/2011. I guess it does forecast to 24 months. What is odd is that they let you run to 24 months though if you never reach the mileage. How is the customer supposed to know the car needs a change once a year (as suggested) when the manual states the car will alert you when it needs service? :dunno:

guerilla twang
03-23-2010, 12:36 PM
Dude, you are amazing. I don't know how or where you got this, but thanks!

furby076
03-23-2010, 12:41 PM
Dude, you are amazing. I don't know how or where you got this, but thanks!

I just googled "The man is watching you" and then went to google images. Not really that amazing, actually.

Bcube
03-23-2010, 12:56 PM
Yup, my countdown starts at 18K miles every time it is reset. The 15K mile mantra comes from the misunderstanding that our E9x CBS follows the previous gen's Inspection I and Inspection II schedules.

The HACK
03-23-2010, 01:02 PM
This has been common knowledge since ~2000, no?

DSXMachina
03-23-2010, 01:14 PM
This has been common knowledge since ~2000, no?

Crikey, it's the first I heard of this. Are you saying we knew that:
1. Oil change intervals are based on how you drive the car which is based on MPG?
2. Your MPG figure is stored in the ECU and could be used by BMW as an inference of how you drive your car?

Speaking for myself, it wasn't common knowledge.

DSXMachina
03-23-2010, 01:19 PM
Hack, as long as I have your attention, there is something I was wondering about. I doubt that current BMW VVT is spline controlled, it must be the vane type (like a torque converter). Are the cams both advanced and retarded by oil pressure (four way spool valve? pulse width modulated solenoid?) or can they only be pressurized in one direction? Anything you can steer me to is appreciated.

Bcube
03-23-2010, 01:23 PM
I believe CBS was introduced around September 2003 for gas engines, March 2003 for Diesel. The E65 7 series was one of the the first -if not the first - platform.

DSXMachina
03-23-2010, 01:31 PM
I believe CBS was introduced around September 2003 for gas engines, March 2003 for Diesel. The E65 7 series was one of the the first -if not the first - platform.

I know about Condition Based Service, I just didn't know the details about which conditions it was monitoring. Did you?

Bcube
03-23-2010, 01:56 PM
I know about Condition Based Service, I just didn't know the details about which conditions it was monitoring. Did you?

WRT your 2) statement, I will say no I did know that MPG was electronically "kept" - although that doesn't surprised me. I had "heard" that how many times one bounces off of redline is recorded. But never found support for that.

WRT your 1) statement. Yes, I knew mpg was a primary input to the Oil Change remaining indication. I embarrassed myself by bringing the car to the dealer around Aug/Sept 2007 and asking for the 15K mile oil change. That was when I learned about CBS (I was 3K miles early) and further research led me to "based upon mpg".

But I hadn't read the SIB you posted since obviously July 2008 as I didn't realize it was updated.

{EDIT} Here is an earlier version of SIB 12 25 05. Sorry I don't know if this is the original or a revision before 7/08. Possibly original as it is pre-N54.


CBS4 was first introduced with the E90 and it differs from the previous CBS2 and CBS3 systems in regards to how the "Engine Oil Service" is calculated.

The CBS4 starting point, of 25,000 km or 15,534 miles for engine oil, is initiated during the PDI - QC1 Handover Inspection with the entry of the "Date of Registration" or after a CBS reset. The Instrument Cluster will round up this data value sent from the DME and begin with a display of 16,000 miles. The countdown until "Service Due" for engine oil is based primarily on the fuel consumption value as calculated by the DME.

The CBS4 algorithm in the DME uses the following fuel consumption averages to achieve the 15,534 target oil service mileage.

N52 with automatic transmission = 21.4 mpg

N52 with manual transmission = 21.7 mpg

Actual fuel consumption above or below these averages may increase or decrease the target service mileage accordingly.

The displayed mileage until service is due, beginning at 16,000 miles, will decrease in 1000 mile increments until approximately 5000 miles remain. It then decreases in 100 mile increments until 500 miles remain, and finally in 10 mile increments until due.

AzNMpower32
03-23-2010, 02:15 PM
I thought this was something BMW has done for a long time. I know for my X3 and that computer system, service was due every 2500 litres of fuel consumed.

boltjaM3s
03-23-2010, 02:17 PM
There's been a lot of discussion in the past about how often we should change our oil. We've also talked about how BMW has an official 15,000 mile interval, or one year, whichever comes first policy.


36 Month Lease + Ultimate Service + 50k Warranty = Who Cares?

I hope my engine seizes at 35k miles. They'll just give me a new one.

BJ

DSXMachina
03-23-2010, 02:25 PM
(snip)

{EDIT} Here is an earlier version of SIB 12 25 05. Sorry I don't know if this is the original or a revision before 7/08. Possibly original as it is pre-N54.

Got it, thanks. :thumbup:

Nordic_Kat
03-23-2010, 03:41 PM
Please forgive my ignorance, but this is my first computerized vehicle and my understanding of engine wear/ oil change intervals is based on lower technology vehicles.

How do these equations factor in not only drive style but general usage patterns? Correct me if I am wrong, but back in the old days short distance city driving was considered the hardest thing on an engine and could cause premature breakdown of oil, no?

So now, we have formulated oils that have all sorts of engine wear protectants built in.
From what you are saying, if the mpg average is factored in, time interval is factored in, but the car will reset if the mileage interval isn't met, etc. etc. My driving habits are going to cause the computer to implode.

Low mileage/short trips/low mpg (at this point 20.2 mpg).
Please elaborate.
Thanks.

R1200
03-23-2010, 07:39 PM
This sounds too simple to me, like some Marketing PR. There are a lot of variables available to the computer that are equally valid and important not to mention the actual oil level/conductance sensor. Fuel consumption is one factor linked to oil dilution but heat is another factor that kills oil.

This explanation of fuel consumption being the major determinant is too simple and if true then I don't trust the results which further justifies my reasoning that more frequent oil changes are required.

Klamalama
03-23-2010, 08:02 PM
This has been common knowledge since ~2000, no?

Yup.

jummo
03-23-2010, 08:11 PM
You guys don't suppose the car keeps track of how many times it deployed the speed governor?

:eek:

Hypothetically yours,

jummo

DSXMachina
03-23-2010, 08:31 PM
You guys don't suppose the car keeps track of how many times it deployed the speed governor?

:eek:

Hypothetically yours,

jummo

Congrats on a thousand posts jummo! Heck, it wouldn't surprise me if the car kept track of how many times we spilled a coffee or tonic in the car.

jummo
03-23-2010, 09:28 PM
Congrats on a thousand posts jummo!

Thanks! How 'bout that me!

I guess this pretty much shows those guidance counselors in High School who told me I was a
bright underachiever who wasn't going anywhere unless I learned to apply myself.

1,000 posts!

Boo Yah!!

And it only took me 8 years.....


jummo

TGray5
03-23-2010, 09:44 PM
Crikey, it's the first I heard of this. Are you saying we knew that:
1. Oil change intervals are based on how you drive the car which is based on MPG?
2. Your MPG figure is stored in the ECU and could be used by BMW as an inference of how you drive your car?

Speaking for myself, it wasn't common knowledge.

Yeap, oil changes came up pretty quickly on my e46 M3 that saw a lot of 'driver education' time. BMW never said a peep about it. :)

TGray5
03-23-2010, 09:46 PM
Please forgive my ignorance, but this is my first computerized vehicle and my understanding of engine wear/ oil change intervals is based on lower technology vehicles.

How do these equations factor in not only drive style but general usage patterns? Correct me if I am wrong, but back in the old days short distance city driving was considered the hardest thing on an engine and could cause premature breakdown of oil, no?

So now, we have formulated oils that have all sorts of engine wear protectants built in.
From what you are saying, if the mpg average is factored in, time interval is factored in, but the car will reset if the mileage interval isn't met, etc. etc. My driving habits are going to cause the computer to implode.

Low mileage/short trips/low mpg (at this point 20.2 mpg).
Please elaborate.
Thanks.

short distance trips and city driving= lower mpg= more frequent oil change intervals

dakarm
03-23-2010, 09:51 PM
This has been common knowledge since ~2000, no?

i concur. i read about it back in 1998-199

mecodoug
03-24-2010, 06:43 AM
I do recall reading that is based on the gallons of fuel used not the miles or any sensors a while back.

I believe the '1 year' recommendation for the US (and seemingly 24 months elsewhere) is similar to my last car - it 'recommended' 7500 mile oil change intervals in the US owners manual and 12000 mi (20,000 KM) in the european manual (requiring the same oil spec for each.)

In my opinion this is because either 1) USA is culturally disposed to think we need more frequent changes and the mfg thinks it may be a credibility issue, or 2) a nod to the dealer service dept for more business (or both) but it is obviously not based on engineering analysis. I supplose some might argue that the warranty may be longer in the USA, and that drives the difference.

I don't know about any of that, but oil changes are so easy (especially in the E90) I have always done them at twice the recommended interval. For my E90 with almost all highway drives of over 50 miles, that is every 10K (the ECU tells me 20K.)

KAP8
03-24-2010, 06:52 AM
Very interesting. I tend to drive very gently. I guess that is why the indicator is telling me that I don't need an oil change until I get to about 19,000 miles.

Stinger44
03-24-2010, 06:55 AM
Intervals based on time have been very beneficial for me since I store my car for the winter. I'm getting oil changes in between less mileage. Not saying that's a good method but it does help in my case for the most part.:cool:

furby076
03-24-2010, 07:25 AM
@Stinger44 - your avatar is painful.

Stinger44
03-24-2010, 07:37 AM
@Stinger44 - your avatar is painful.
Hmm, she was prom queen at BinFarteen HS in Mumbai. Perhaps the western world isn't quite ready for Southwest Asian beauty queens.

Nordic_Kat
03-24-2010, 07:38 AM
short distance trips and city driving= lower mpg= more frequent oil change intervals

That's what I thought, but based on the tidbit of "if you don't reach the mileage in the estimated interval the counter recalculates..... ", it would seem like I'm dooming my car if I rely on it to keep track of when it needs the oil changed.

magbarn
03-24-2010, 08:25 AM
This has been common knowledge since ~2000, no?

Coming over from E46 land, I was also under the impression that my '03 330i based the OLM solely on MPG. I also thought the E46 323i/328i, had a more complex system (calculated also on number cold-starts/rpms etc) that they "dumbed down" for the 325i/330i engines.
AFAIK, GM/Honda OLM's also use the same calculation as per automotive journals I've read in the past on Oil Life Monitors. (BTW Honda has a sweet OLM as it will also calculate ATF change intervals based on number of shifts & tranny oil temps)

vadim
03-24-2010, 10:37 AM
Please forgive my ignorance, but this is my first computerized vehicle and my understanding of engine wear/ oil change intervals is based on lower technology vehicles.

How do these equations factor in not only drive style but general usage patterns? Correct me if I am wrong, but back in the old days short distance city driving was considered the hardest thing on an engine and could cause premature breakdown of oil, no?

So now, we have formulated oils that have all sorts of engine wear protectants built in.
From what you are saying, if the mpg average is factored in, time interval is factored in, but the car will reset if the mileage interval isn't met, etc. etc. My driving habits are going to cause the computer to implode.

Low mileage/short trips/low mpg (at this point 20.2 mpg).
Please elaborate.
Thanks.
City driving results in low MPG. So do short trips. So does a heavy right foot. Combine any of these, and the MPG will drop even more.

Conversely, constant speed long distance highway cruising at moderate speeds results in high MPG readings.

So, all in all, this method is fairly adequate for engine wear evaluation.

DSXMachina
03-24-2010, 10:41 AM
Hmm, she was prom queen at BinFarteen HS in Mumbai. Perhaps the western world isn't quite ready for Southwest Asian beauty queens.

Burned! I just Googled BinFarteen HS in Mumbai and there is no such place! Better level with us Stinger, who is this mysterious and exotic woman?

Stinger44
03-24-2010, 11:25 AM
Burned! I just Googled BinFarteen HS in Mumbai and there is no such place! Better level with us Stinger, who is this mysterious and exotic woman?
Hah, google doesn't work in India!

The HACK
03-24-2010, 11:28 AM
Coming over from E46 land, I was also under the impression that my '03 330i based the OLM solely on MPG. I also thought the E46 323i/328i, had a more complex system (calculated also on number cold-starts/rpms etc) that they "dumbed down" for the 325i/330i engines.

You would think if ANY of BMW's car would have a fancy TRUE condition based interval, it would be the top of the line M cars.

WRONG.

They're all based on the amount of gas consumed. If I recall correctly, for the 323i it was around 660 gallons. For the E46 M3 it was around 500 gallons.

When the E9X first came out people were so damn sure that BMW has upgraded their "condition based" interval for the oil based on some fancy sensor and oil analysis. When RealOEM finally had E9X diagrams available and the oil level sender were no more fancier (and expensive) than the E46 oil level sender that pretty much concluded the discussion I thought.

Stinger44
03-24-2010, 11:30 AM
Okay, due to the death threats from other posters, I uploaded my HS sweetheart pic. There, happy now!

The HACK
03-24-2010, 11:32 AM
...Are the cams both advanced and retarded by oil pressure...

Yes. At least when my mechanic buddy was working on replacing a Double VANOS unit on an M54 he indicated that the unit works similar to how a CVT works. Oil pressure expands and contracts a gear sprocket on a chain driving the VANOS unit.

Does that help or am I thinking of something else?

speedy_sam
03-24-2010, 12:59 PM
To the OP, thanks for the informative post!

DSXMachina
03-24-2010, 02:19 PM
Yes. At least when my mechanic buddy was working on replacing a Double VANOS unit on an M54 he indicated that the unit works similar to how a CVT works. Oil pressure expands and contracts a gear sprocket on a chain driving the VANOS unit.

Does that help or am I thinking of something else?

Sounds like that would be the case. That way the cams are bicontrollable. At one time, when there was no OP (engine off) the cams went to 'zero' (by spring pressure) and the oil pressure would move them in one direction only. Now the cams can be regulated advanced and retarded as required.

DSXMachina
03-24-2010, 02:25 PM
Okay, due to the death threats from other posters, I uploaded my HS sweetheart pic. There, happy now!

There's a lot to be said for the natural look. Did your real HS sweetie have amblyopia? It looks like she might. I find that an attractive trait, sort of like Jewel's smile. But instead of the teeth going in different directions the eyes do.:thumbup:

The HACK
03-24-2010, 02:31 PM
Sounds like that would be the case. That way the cams are bicontrollable. At one time, when there was no OP (engine off) the cams went to 'zero' (by spring pressure) and the oil pressure would move them in one direction only. Now the cams can be regulated advanced and retarded as required.

Only when the oil reaches operating temperature I was told (something like 89 degrees celcius. My mechanic even showed it to me on the GT1).

rrosen
04-02-2010, 10:06 AM
Probably the most sophisticated oil life system (at least that I'm aware of) is from GM. It measures a lot more than MPG. I know it uses RPM and temperature plus probably more things. There have been a few SAE papers published on their patented technology. Not to mention some SAE awards.

Basically they measured a lot of cars under controlled conditions, analyzed the oil, and from that determined some equations that used RPM, time, temperature, etc., to come up with a result that indicated the condition of the oil. They then used that to trigger the alerts.

There's a brief summary below.

Oil Life Monitor Stripped Bare

(reprinted from General Motors)

The patented engine oil change technology involves computerized monitoring of engine revolutions, operating temperature, and other factors to optimize the change interval selection. The typical recommended interval for gasoline-fueled passenger cars and light-duty trucks is 3,000 miles (4,800 km) or three months, whichever first occurs, when outside temperatures are below freezing and trips are short. These conditions are considered severe duty. For ideal driving conditions, relating to long trips with mild outside temperatures, the interval can be expanded to 7,500 miles (12,000 km). Starting with the 2000 model year on certain vehicles, GM will raise the maximum mileage allowed for Oil-Life System-equipped vehicles to between 10,000 and 15,000 miles (16,000 and 25,000 km), depending on vehicle brand and engine*.

The development of the Oil-Life System began over a decade ago by researchers Shirley Schwartz and Donald Smolenski, both of the GM Research Laboratories. They discovered, through various investigations, that oil degradation, in general, followed pathways influenced by service and environmental conditions. The extremes of these conditions, as shown in Figure 1, are high-temperature, high-load on one end and low-temperature, low-load on the other. In between is the large operating domain representing the majority of driving conditions. The basic design of the Oil-Life System was intended to characterize extreme operating conditions and most points in between. While the Oil-Life System does not actually monitor any single quality or physical property of the oil, it does incorporate the use of a highly sophisticated mathematical model. This model applies the known influence of oil service temperature and revolutions to characterize the remaining life. The influence of temperature, in particular, has a marked impact on oil life. The almost parabolic nature of the aging rate with temperature emphasizes the importance of this as dependent variable. On the other hand, time or running time (in the absence of mileage or engine revolution data) was not found to be a particularly good indicator of oil life, since it did not adequately distinguish between periods of extended idle and periods when engine speed was high.

The onboard calculation of oil age was simplified by using penalty factors (as opposed to equations). A penalty factor is an indication of the rate of oil aging at a given operating temperature. For any given oil, higher penalty factors are associated with faster oil-aging rates. The model uses engine revolutions as a basis for measuring duration of service. Gathering the data to show correlation of on-board measurements of oil-change intervals to laboratory oil analysis is a slow process, requiring months or years. For example, a typical short-trip service test can last two years. During the original research program approximately 130,000 kilometers were accumulated in determining the constants for the mathematical model and another 160,000 kilometers were logged in testing vehicles equipped with the Oil-Life System. The four oil analysis tests are:

1. Total Acid Number (TAN)-Concentration of acid constituents in the oil from oil oxidation and combustion products.
2. Total Base Number (TBN)-Depletion of overbase detergent additive.
3. Differential Scanning Calorimetry (DSC)-Approximates the remaining life of the antioxidant (residual oxidation induction time).
4. Pentane Insolubles (PIN)-Concentration of carbon soot and sludge.

The point at which the oil-change indicator signaled an oil change is then shown. All oil analyses results are plotted, including those data points regarded as "outliers", that is, points with values differing by more than approximately 20 percent from the trend lines from all data. It is interesting that DSC data followed a rapid decay curve from the outset. Also interesting is that both TAN rises and TBN falls at an apparent increased rate near the point where PIN rises (about 16,000 km). Even though not all of these changes occurred with each vehicle and there was usually some oscillation in the data, it was still possible to use these generalizations as guidelines to characterize the oil aging process.

From these studies and other subsequent investigations it is clear that there are distinct benefits to drivers of vehicles equipped with the oil-life monitoring systems. For those who neglect to change their oil on a regular basis, the system provides reminders that a change is due. If they need the reminder and follow through with an oil change, they'll protect their engine from premature wear. And, drivers who thought they needed to get their oil changed every 3,000 miles (5,000 km) or so, might be able to go longer between changes. This will save them money, time, and perhaps more importantly, precious natural resources.

Ref: Schwartz, S. E. and D. J. Smolenski, "Development of an Automatic Engine Oil-Change Indicator System," SAE Paper 870403.

* General Motors has set the maximum distance for normal driving on the Chevrolet Avalanche equipped with the 5.3 liter and 8.1 liter V-8 gasoline powered engines at 10,000 miles.

Author Credit: General Motors Corporation

Saintor
04-02-2010, 11:16 AM
This sounds too simple to me, like some Marketing PR. There are a lot of variables available to the computer that are equally valid and important not to mention the actual oil level/conductance sensor. Fuel consumption is one factor linked to oil dilution but heat is another factor that kills oil.

This explanation of fuel consumption being the major determinant is too simple and if true then I don't trust the results which further justifies my reasoning that more frequent oil changes are required.

Fuel consumption can't be the only one; they are many variables.

Here's a very good sum up.
http://www.machinerylubrication.com/Read/562/oil-change-filter-sensors

Here's what is likely to be in our cars.
http://www.conti-online.com/generator/www/de/en/cas/cas/themes/products/powertrain_and_chassis/measurement_systems_en.html

Continental Temic Microelectronic GmbH QLT Oil Condition Sensor
The QLT sensor was launched in 1996 to monitor engine oil quality, level and temperature. Two sensors simultaneously and continuously monitor diesel engine oils containing soot. The instrument also monitors nitric oxide and oxidation products in spark-ignited engines, as well as water and fuel contamination. Because these factors influence the oil***8217;s electrical properties and permittivity (ability of a material to resist the formation of an electric field within it), an effective oil condition sensor is achieved, according to the manufacturer.

DSXMachina
04-02-2010, 11:21 AM
Interesting reading rrosen. It's amazing how sophisticated our cars have gotten. To wander a little OT, although it does relate to the technologies available today, Toyotas have gone off the deep end. The Prius, beginning in 2008, has a "Plasmacluster Ion Generator"! No, I'm not making that up and it's not April 1 anymore.
It's a device "provided inside the air duct of the side register on the driver's side to improve the air quality and comfort in the cabin." The damn thing operates at such high voltages (like Xenon headlamps) that reaching into an air duct could be the last thing a tech remembers before waking up in the hospital. I want hazardous duty pay.

Weaselboy
04-02-2010, 12:06 PM
Fuel consumption can't be the only one; they are many variables.

Here's a very good sum up.
http://www.machinerylubrication.com/Read/562/oil-change-filter-sensors

Here's what is likely to be in our cars.
http://www.conti-online.com/generator/www/de/en/cas/cas/themes/products/powertrain_and_chassis/measurement_systems_en.html

Saintor>> I doubt our cars have a device like this for two reasons. When we get a "low mileage oil change" (once a year) in between CBS called for oil changes, the dealer does not reset anything yet the mileage until oil service stays the same and keeps counting down. If there were a sensor as you describe the sensor would detect new/fresh oil and move the mileage until next service up, and that does not happen. Also, engine parts lists like realoem do not show a sensor like you describe in the engine.

Saintor
04-02-2010, 12:55 PM
I am 95% positive that it has one.

See item #4 here.
http://www.realoem.com/bmw/showparts.do?model=VH13&mospid=49545&btnr=12_1139&hg=12&fg=05

The shape is very similar to the Continental ATE device I referred to (there was a pic before on this page - gone).

galahad05
04-02-2010, 01:31 PM
I heard the same thing as Saintor. Somewhere on my laptop's hard drive I saved off a BMW-spec'ed document that talks about the capacitive oil condition sensor, with theory of operation and diagram. I wonder where I put it...

Weaselboy
04-02-2010, 02:31 PM
I am 95% positive that it has one.

See item #4 here.
http://www.realoem.com/bmw/showparts.do?model=VH13&mospid=49545&btnr=12_1139&hg=12&fg=05

The shape is very similar to the Continental ATE device I referred to (there was a pic before on this page - gone).

Although it is labelled "oil leveling sensor", you may very well be correct. I still can't see how this sensor would account for the between CBS annual oil changes. :dunno:

galahad05
04-02-2010, 05:51 PM
I guess just because the car has an oil condition sensor doesn't mean the engine control software has to really listen to it, or very much.

Scenario:
Engineer: Sir, we've put in an capacitive oil condition sensor which can really help tell us when the oil's gone bad. Nice feature, right?
Boss: Achtung! Dumkopf! Don't you know that WE have to pay for these oil changes now? Make them one year intervals. That's good enough. Ignore the sensor.

madone E92
04-02-2010, 06:44 PM
I don't care how BMW calculates the interval. I get oil and filter changed every 6,000 miles and therefore pay for some changes.

Saintor
04-02-2010, 06:53 PM
I guess just because the car has an oil condition sensor doesn't mean the engine control software has to really listen to it, or very much.

It sure does.

One of my oil changes was required by the system at 16000km instead of the usual 21-23000km. Of course, my fuel consumption was not higher by 15-20%. Now it seems to be back to normal for this one.

bmw325
04-03-2010, 05:43 AM
e46 worked the same way...the Bentley manual even mentions it. I think prior to the e46 (on cars that had the green/yellow/red light bars for service) BMW used a more complex algorithm...then I guess someone figured out that mpg was a good proxy.