nam_cruze

hey everyone...!! I own a toyota double cab ss rx 206. Ive noticed recently that even few miles after a oil change, the oil goes dark in colour and is thicker than usual...!! the oil that i am using is DS40..!! does this mean that there is sludge buildup in my engine or am I using the wrong oil...??? I don't know if this is a rookie question but any help would be greatly appreciated.... thanks!!