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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing / Warranty > Oil level sensor



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      04-03-2014, 08:05 PM   #1
rborane
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Oil level sensor

My oil level on my 335i showed that it was 1/4 of a quart low, so I put in 1/4 of a quart of oil, and the level hasn't changed after driving around. Do I need to reset anything or does it just take a while to register the added oil?
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      04-03-2014, 08:22 PM   #2
I6TT
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are you remeasuring it in iDrive?
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      04-03-2014, 09:29 PM   #3
vandalbob
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Probably just takes some time. On one of my oil changes I checked the level immediately after pouring in the oil and the indicator said to add 1 qt although I knew I had put in enough oil. The next morning the indicator showed I had enough oil. Go figure. One of the techs at the dealership said he'd regularly seen that.
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      04-04-2014, 06:36 AM   #4
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It's not that simple. First off, BMW recommends only adding top-up oil in 1 quart increments when the CBS gives notification that the engine is 1 quart low. The reason this is is because the system only reports oil level in 1/4-quart increments, so you can be between 1/2 quart low and 1/4 quart low and the system only reports 1/4 low because the engine oil level is between 1/2 and 1/4 quart low (i.e. not a full 1/2-quart low). So adding in only 1/4 quart may not get it to report "full". The system does not behave instantly like a mechanical dipstick does, where you immediately see a change in the oil level on the dipstick. When the engine reaches 1-quart low, it notifies you immediately, which means the engine is not more than 1-quart low. When you periodically read the e-dipstick and it reports it is 1/4-quart low (for example), it may be more than 1/4 low but not yet a full 1/2 quart low; meaning it could be several thousand miles at 1/4 low and you never knew it (because you didn't check the e-dipstick right when the system determined the engine was 1/4 low) and by the time you did check the engine is almost 1/2 quart low. This is why the owners manual says to top off the engine with 1 full quart when you get the "+1 qt" notification within the next 125 miles.

Secondly, the oil level measuring system reads the last reported oil level until such point where operating conditions allow it to determine a new reading. The system monitors oil level on 5-minute increments once the parameters have been reached (time and oil temperature) to determine a measurement, so it doesn't instantaneously report the new oil level, which is why it is best-practice to only top up in 1 quart increments, when the system notifies you because you can over fill the engine when trying to top off at 1/4 increments.

The oil level sensor is not a "direct-read" device (i.e. like a float) but rather a system that collects data and then interprets the data to display a report on the oil level; it is all software driven.

Last edited by Efthreeoh; 04-04-2014 at 06:44 AM.
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