This is an indication that your oil pressure sender has gone south. Mine did the same thing....and the needle remains pegged no matter what the conditions.

Get a replacement from FastLane...about $65...and a 10 minute DIY replacement...

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car