BMW oil change sensing system

[TambourineMan]

I was asking my dealership how much they charged for an oil change ($130) and whether they ever took oil samples for analysis. The answer was "no - they were not needed as BMW's have sensors that determine whether the oil is still good or needs to be changed."

In some other threads I think I read that the sensors don't really check the oil, but rather all they do is measure the gallons of gas consumed at different operating temperatures (that is, it measures the amount of gas consumed while the engine is cold or very hot versus when just normally hot since presumably the oil can deteriorate faster if you do a lot of short trips or really push your car hard.

(You'd think BMW would have some sort of quality control feedback check to determine if their system actually works. How can BMW be sure that whatever system they are using is actually effective unless they double check from time to time with actual oil analysis?)

Does anyone know how a BMW car gets the information to tell you that the oil needs to be changed?

[promp3]

It just goes by run time, what you read is probably correct, its not a prescise science, becasue oil changes are not a precise science. I dont think there is a sensor that tests the oil, if there is than its news to me. Dealerships like to tell customers things that make them think bmws are the most high tech thing sence the space shuttle, it makes the customer feel good. Bmw knows that as long as people are'nt driving 20k on a single oil change that they probably won't have to write any warrenty checks. just rember It won't kill you to change the oil before the life indicator is in the red. if you want your engine to be clean and healthy for its intire life, sooner is better than later.
use synthetic oil of the correct viscosity, thats all you need to do and all your engine needs.

Its not like a doctor sending a poo sample off to the labs to see if you have butt cancer. what will them testing the oil tell you? that it needs to be changed after 2.5k? well that seems like useless information to me.

If it makes you feel any better about the price it costs me about $80 to change my own oil.

[TambourineMan]

I have no problem paying $130 to have the dealer change my oil at a 7,500 mile mark that does not come on the free maintenance schedule.

I have attached (I think - I have not done an attachment on this forum before) info on the N54 oil sensors.

what I don't understand from it is whether a simple electric conductivity test is sufficient to detect a problem from gas getting into and diluting the oil.

Here is the key info from it:

Oil condition sensor
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 aging.

Measuring method
The oil condition sensor consists of 2 cylindrical condensers. The ondensers 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).

[v1nyd]

my bmw tells me to get an oil change when i read the little sticker on the top corner of my windshield from avis lube that says XXX,XXX miles or the date 3 months after i did the oil change =P

[lhgubi]

There has always been questions about oil changing. I found if you are using conventional oil change it every 3K miles under normal driving conditions. (not tracking or street racing). If you are using synthetic, then change it every 5K. If you want to go by what the dealer says, the engine will most likely last a long time, but I change the synthetic oil every 5K. I think my E36 is faily young with 106K.

I own a reset tool, but you do not NEED to reset the indicator. DON'T try to short out the pins on the computer connector. If you screw up it can blow the DME.

[ptarditi]

We have an e36 (m42) and e46 (m54) and we change our oil every 7500mi, but I change the paper filter element every 3-3.5 k. They are very accessable and relatively cheap. i am also running Royal purple in both. The OEM Syn is fine, but since I work at a dealership I don't want to hear from management that I might be stealing their oil. The e30 gets its oil changed every 3-5k also, but usually every 6 mos. as it doesn't get driven nearly as often.

[tsweers89]

why pay so much for a oil change. just do it yourself youll be saving so much $$$ and its def a DIY

[TambourineMan]

I have asked this question before on several forums and still have not received an answer.

I probably will not change my own oil, but if I did I would want to use a better, but approved oil than what the dealers use. In fact, I might want to give them a better oil to use instead of the OEM oil.

I don't have the actual manual for my car yet as it has not yet been delivered. I downloaded the 2007 335xi coupe manual (which should be the same) and what it says is (UPPER case added for emphasis):

"If BMW high performance synthetic oil is NOT AVAILABLE, you can add SMALL quantities of other synthetic oil. Only use oils with the API SH specification or higher.

Your BMW Center will gladly answer any questions regarding . . . [other] APPROVED synthetic oils. . . .

. . . APPROVED oils belong to the 5W-40 and 5W-30 classes."

The manual says info on approved oils can be found at www.bmwusa.com but I could not find it there, nor could the customer service rep point me to where it could be found. they told me verbally some that were approved, but what good is that 3 or 5 years from now - I did not record the conversation.

I want to know where to find BMW's official published information on the specific brand names, specifications, SAE rating, etc.

For instance I have read that the US brand of Castrol synthetic is not approved, but the German Castrol is approved and is said to be re-badged as the BMW OEM oil.

I am seeking official information in writing from BMW (not from Mobil, not some other oil company as they do not warranty my engine) as to specifically which brands, SAE viscosity ratings, specifications (ACEA A3, LL 01, AOI SH, etc.) etc. are approved by BMW.

[promp3]

We have an e36 (m42) and e46 (m54) and we change our oil every 7500mi, but I change the paper filter element every 3-3.5 k. They are very accessable and relatively cheap. i am also running Royal purple in both. The OEM Syn is fine, but since I work at a dealership I don't want to hear from management that I might be stealing their oil. The e30 gets its oil changed every 3-5k also, but usually every 6 mos. as it doesn't get driven nearly as often.

I will never go that long with out an oil change even if I am using oil that says it made for it. I change around every 3k even with synthetic. Id just rather keep the oil clean than go a little farther per oil change. my bmw dosent get driven as much becasue it is a second car so it dosent happes so often but but for people that drive a ton a month I can see haw it can get agravating. I just like the peace of mind that when I am red lining my engine the oil is fresh.

[ptarditi]

Lots of technology has apparently passed you by. The oils are much better, the fuel is much cleaner and the metallurgy has improved greatly. When they took the lead out of the fuel everyone thought that you would need a valve job every other year. When they stopped using pure brass bearings a motor could go further then 500 miles before a rebuild. Just imagine the debate raging when Grandpa went and doubled his time between bearing changes. BMW OEM oil is a Castrol product, used to be made from the castor bean. Castrol has been linked to BMW thru racing for years there was a time when GTX was the universal oil used by all hard driving bimmerheads. Carbuerated engines and early k-jet cars had a tendency to over fuel the cylinders and this would cause an early degradation of the oil. 2% CO was considered lean. Also valve guide seals wouldn't last as long as they do now so further oil contaminatiion. the PCV system was even cruder. If you are changing your syn oil every 3k you are wasting resources and performing unecessary maintainance.

[TambourineMan]

ptarditi,

New technology is usually good - when they finally get it right. BMW has not always got it right the first time - for example the fuel pump seals on the E9x's not being able to handle the ethanol that tree huggers and donation seeking pols insist on adding to our gas.

Before you poo poo more frequent oil changes, you may want to review these threads:

http://www.bobistheoilguy.com/forums...&Number=981164

http://www.bimmerfest.com/forums/sho...d.php?t=266893

In the first thread, there is info that the oil was bad after just 1,000 miles.

The 335 engine is only 2 years old and is BMW's first gas turbo in a long time. In my layman's opinion it takes longer than that to determine if 15k oil changes are adequate for engine longevity. If you are leasing, no problem. But I am buying. $130 here and there seems like a prudent policy.

My purpose in this thread was not so much DIY oil changes or their frequency, but to determine the adequacy of BMW's system to determine when the oil needed to be changed under the maintenance program.

[Shivan000]

Holy crap thats a lot of money for an oil change!

I did mine over the weekend, took me about 20 minutes in 30° weather and it cost me about $45 for the filter and five quarts of fully synthetic oil.

[ptarditi]

Diesels run at higher temps under much more extreme conditions than Spark ignition engines yet they have extended oil service intervals. If BMW thought for one moment that they were putting their motors at risk they wouldn't recommend these intervals. As I said I actually have the interval on my own vehicles. Also I have seen them goodwill motors at over 100k as long as they have followed recommended service intervals. I would be more concerned about the abuse these motors take that are only run for very short times that don't allow for the burning off of condensate. 3k oil services with syn oil is more than anal. Sorry I run high mileage bimmers from 132k to over 250k on the 325es and as I siad before you are completely wasting your money, change the filter yes, let the oil run longer. In fact the main enemy of the BMW motor is its cooling system so if you are going to spend money any where thats the place. Cooling systems have been a problem since the iconic 2002, the first big sixes warped heads not due to oil, but due to cooling inadequecies.