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.

A mechanic cracked open a neglected engine and what he found was brutal.

This may sound like something out of the original "CSI: Crime Scene Investigation" TV series, but you can tell a lot about engine health by pulling out the dipstick, reading the oil level, and ...