Sooo.. what makes old oil black? It is little parts of your engine in the oil, like fine metal dust? Is it from the oil getting too hot? Is it from the heat cycles of going from cold to hot, back to cold over and over that make the oil change is some way? Or something else?

Just wondering what really makes oil go bad over time.

 

Heat

 

its from the carbon deposits your engine makes when you burn gasoline. Dirt can also make it black. Black oil is common in older engines (100k+ miles) and its ok, it just means its doing its job....cleaning your engine

 

so it's from blow down gasses then. Thanks...

 

put a lighter to some oil. give it enough time and it will turn dark.

 

black paint will turn it black too.

 

if your oil doesnt turn black then your motor oil isnt doing it job cleaning the inside of the motor.