check and see if your engine is still under warranty. If yes then bring it to a nissan dealer. They are going to check your oil and if its looking dark grudge then they are going to check if you have done your oil change routinely. They most likely will say they are going to take the engine apart and see if its like super dark and if it looks like you haven't got a oil change for years. If anything just show some receipts that you have gotten your oil change routinely. After that they most will replace your engine
. That's what happened to me.