Engine oil color reveals its age, contamination level, and operating condition. Fresh oil is amber or light brown. Oil darkened to black but still translucent after a few thousand miles is normal.

Engine oil turns black from a combination of combustion byproducts, heat oxidation, and detergent additives suspending c ...

I had the radiator serviced on my car; just preventive maintenance. I noticed on the repair invoice I was charged for a cooling system additive.