the gauge is run from a sensor on the oil filter tower, that sensor has failed on your engine.

In normal condition the gauge is pegged with cold oil and is in the middle with warm engine at idle, stepping on the gas will make it peg again.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)