How to Discolor Used Engine Oil

1. Drain old, used oil from the car and contain it in a sealed bucket or jug. Used motor oil is a pollutant that can harm the environment, so it needs to be stored in a container it will not leak from.
2. Pour a gallon of your fluid into the old oil, using a funnel to avoid spilling it. Water, antifreeze and similar water-based fluids will all change the color of the oil. Water is the best choice because it is not a pollutant or toxic to the environment and engine oil will mix with water, though it may separate if left to sit for long periods.
3. Stir or shake the oil and water mixture. The oil should take on a lighter, milky color and may bear a resemblance to a chocolate milkshake in terms of color and consistency. If the oil is still too dark, continue adding water.