- Mar 15, 2006
- Buffalo, NY
I'm sorry if this topic has been discussed before, but I've noticed that oil seems to look blackish if checked when cold, and when the car is at operating temp., it tends to return to it's goldish state or at least a dark brown even after 3 or 4K... Can one of you industry guys explain this? I suspect that the unwanted deposits and bi-products of combustion are suspended in the oil when cold, then sink to the bottom of the sump as the oil is warmed? Is this why every manual I've ever read tells me to check my oil when the car is hot, and been turned off for at least 10-minutes? Is this also why oil should only be changed when warmed?