Anyone Know how the Oil Level Sensor Works?

[alpinecoupe]

I know there are A LOT of threads on the oil level issue.

Here is my story:

Oil level at top arrow when new.
Dropped to 8/10 mark at 1200mi service.
Picked car up from dealer, level at mid-mark.
(I questioned them and they said "That's where it is supposed to be, at the half way mark.") Not happy with answer.
I drove the car for 150 miles and added 250ml.
No change.
Drove the car for another 150 miles and added an additional 250ml.
No change.

Then after approximately 800 miles of driving following the service
(mileage then 2K) the oil level read at the top arrow.

Yes, the manual says that the sensor does not detect additions less than 500ml. What I would like to know is HOW does the sensor determine the oil level and WHY did it take roughly 500 miles for it to detect that I had added 500ml?

The car now has 3150 miles and still reads at the top arrow.
I would appreciate any logical explanation for this.

Thanks.

[rcornelius]

Originally Posted by alpinecoupe

I know there are A LOT of threads on the oil level issue.

Here is my story:

Oil level at top arrow when new.
Dropped to 8/10 mark at 1200mi service.
Picked car up from dealer, level at mid-mark.
(I questioned them and they said "That's where it is supposed to be, at the half way mark.") Not happy with answer.
I drove the car for 150 miles and added 250ml.
No change.
Drove the car for another 150 miles and added an additional 250ml.
No change.

Then after approximately 800 miles of driving following the service
(mileage then 2K) the oil level read at the top arrow.

Yes, the manual says that the sensor does not detect additions less than 500ml. What I would like to know is HOW does the sensor determine the oil level and WHY did it take roughly 500 miles for it to detect that I had added 500ml?

The car now has 3150 miles and still reads at the top arrow.
I would appreciate any logical explanation for this.

Thanks.

Good luck, and I mean that. You will even be lucky if you find two BMW dealerships that tell you the same answer. Shitty system that don't work the way it was designed to at least in the M3s. My wifes 07 328 has the basic same system and we have never had any problems with it. Always correct. With the M3 I've gone through the same thing as you. My advice is if it is half way just leave it, nothing wrong with driving the car with it half way. What you don't want to do is over fill it. I'm just hoping that BMW will come up with a fix and take care of this for us pretty soon. Although I will not hold my breath on this.

[alpinecoupe]

Latest Update:

Around 6K, the gauge read at the 3/4 mark.
I opted to take the car in for an oil change at 6600 miles (5.5K after the initial break-in change).
Same story, I picked the car up and it was reading at the half mark.
Again, I assume that the gauge, if linear, reflects a total range of approximately one liter.
I drove the car for 100+ miles and got the same reading.
I added 500 ml.

I drove the car for two days, approximately 55 miles.
When I pulled into my garage I checked the gauge and it was showing the rotating "clock" symbol, indicating that it was recalculating the level.
It then displayed at the top arrow mark, with the OK indication.

Based on this experience I will make the following assumptions:

The service technicians are very nervous about adding too much oil, so they play it conservative and fill it slightly under the maximum capacity.
For some reason (and this is where I am still confused) the sensor does not seem to register small amounts of oil added in a timely fashion.
Referencing my initial post, it took approximately 800 miles before the gauge reflected the 500 ml that I added incrementally.
This time, I added the 500 ml all at once (as noted in the manual) and it registered after approximately 55 miles.

Better, but I still fail to understand why it would not register after the oil was up to full operating temperature, say after 15+ miles of driving.

Bottom line:

I check it each time I drive the car.
There's plenty of oil in there and as long as no flashing red lights come on, I'll live with it.

My intuition tells me that the next iteration of M3 with have this dialed in better. I'm certain that this issue is no secret to BMW.

AC

[sayemthree]

good luck. mine read add one quart - luckily I was hesitant and added only q/2 quart and after a few miles it read full. If I had added the full qt I may have gotten the overfill error.

[alpinecoupe]

Originally Posted by sayemthree

good luck. mine read add one quart - luckily I was hesitant and added only q/2 quart and after a few miles it read full. If I had added the full qt I may have gotten the overfill error.

Yes, I admit to having some hesitation when I made the decision to add the 500 ml.
It was based on previous experience (adding 500 ml at the half mark that eventually brought it up to the top arrow).

Given the enigmatic operation of the oil level sensor it appears that it will always be a matter of making the call to add, or not.

I'm going to see if I can get any information from BMW on this...

AC

[gr8000]

Just empty the 1lt bottle when prompted to do so. Don't add fractions as you may end up ovefilling (= trouble). That's what I was told by my dealer, that's what I did 2 times already with no issues. There is enough oil in the sump for a while even when the oil level indicator shows minimum.