I have a 2009 ML550 with the M273 V8. 90K miles and never used a drop of oil. Oil changes every 5k miles. I've used Mobil 1 0w-40 for years. Last time I changed to Penzoil 5w-30 Ultimate.

Today, I get the oil warning message. I checked the oil 2 weeks ago and it was full and have done maybe 500 miles since then. City driving, nothing taxing. Today it needs just over 1.5 quarts of oil. Last change was 3k miles ago. I spent the afternoon and checked:

No leaks anywhere - its as dry as a bone. Oil pan, front seal, oil cooler, rocker covers, cam plugs, pcv etc all checked and dry.
Pulled all 8 plugs - its not burning it. Plugs were spotless and all in the same condition
No oil burning residue in exhaust
PCV rebreather dry - no oil evident
Oil Cooler seals have been replaced - no oil in coolant
Rear main looks ok - a little moisture but nothing significant
Motor runs beautifully and very smooth.
Doesn't blow smoke on start up or under hard acceleration.
Zero blow-by.
Temprature where I am is cool but not freezing and car is always garaged.

Any chance its the oil? This car has never used a drop and now its gone through 1.5 quarts in 500 miles. Any ideas or similar experiences welcomed.

TIA

 

UPDATE - Mystery solved - For the following two mornings after this event, I've checked the oil and as I thought might occur, its overfull. So I've now sucked out the 1.5 quarts and its back to being on the full mark. This engine always took time for the oil to settle back to the pan, but I didn't think it would show so little and still be below the minimum mark after a few minutes rest. The oil I put in also didn't show up on the dipstick quickly which lead to me to think it needed a fair top-up. It seems I've got an issue with the oil level sensor in the oil pan which triggered the warning message.