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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 01-24-2020, 06:20 AM
mohamedrani mohamedrani is offline
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Location: Russia
 
Join Date: May 2018
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Mein Auto: 520i 1998
Fuel Indicator

Hey guys,
i noticed that when the weather is cold, some where below -5 , when i start the car, the fuel indicator always very low , and if i have for example 15L in the tank , the light for the empty take will light , but as the car warms up, it shows the current fuel correctly, when i fill the tank it goes to the max. normally too, but sometimes it's just little slow, like i've to drive couple of KMs or if i just let the car at home for a day,
is that a bad fuel sensor?
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  #2  
Old 01-24-2020, 11:21 AM
djbecker djbecker is offline
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Mein Auto: e30,e34,Z3,e39
Some background that may help you diagnose the problem:

The e39 has a "saddle tank". The tank straddles the driveshaft. Once the level drops below about 1/2, the two sections of the tank are isolated.

To allow this to work with a single electrical fuel pump, there is a "siphon jet pump" that transfers fuel from the left side to the right side. It is a passive device that uses the return flow from the fuel pressure regulator past a venturi to suck fuel using a tube that goes from the bottom of the left side to the right side.

This has no effect when you have more than a half tank of fuel and the fuel level is above the saddle. Once the level drops below the saddle, the behavior depends on if the fuel pump is running. If it is running, the left side is constantly emptied while the fuel pump is running. When the engine is shut off, the fuel levels equalize through the siphon tube.
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Old 01-24-2020, 11:36 AM
528iAut 528iAut is offline
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Mein Auto: 1996 528i
Quite normal.
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