The oil filter housing also holds probably at least 1/2 quart of oil that will not drain out until you remove the cap and filter. This portion of dirty oil probably remained when you changed the oil.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record