I have heard that this difference from the low notch to the high notch is one quart, but I think this in incorrect. My car was reading about 1/3 of the way up from the lower notch, I added one quart, and it still is below the upper mark. How about yours? I added the quart to attempt to eliminate a nasty engine noise around 1500 rpms, coming from the top-front of the engine, around the VANOS unit, or cam gears. I may be operating here very soon to locate the culprit. BTW, the noise is there above 1500 rpms, just not as loud. At 1500, it sounds like a metallic gurgling. My car has 101,000 miles on it. A friends 325i w/VANOS makes the same noise, it has 120,000 on it.
Are there any concerns with slightly overfilling the crankcase, by this I mean, having an oil level reading above that upper notch in the stick? Any experience would be helpful, as well as any suggestions to the root of this noise.