When I change the oil in my diesel. I do open the drain plug first, then remove the oil filter cover. All this discussion about when and where the oil should be, and yet no one seems to mention the simple way of measuring oil. Check your oil at the same, everytime. Be it stone cold or warm and sitting for 10 min, just be consistent. This way you can determine if your engine is using oil. When I have added the prescribed 2 gal. of oil after an oil change, I start the engine to get the oil pressure up and then shut her off. I check to see where the oil level is after a few minutes and use that as a reference point. The oil may be "cold", but as long as I check the oil under the same conditions, ie "cold", then I can guage any oil usage.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member