Where is the overflow tank on a 99 cadillac deville?

The overflow tank on a 1999 Cadillac DeVille is located in the front of the engine compartment, usually on the passenger side (right side). It's often a smaller, translucent or semi-translucent plastic reservoir. It's connected to the radiator by a hose. However, its exact location might vary slightly depending on specific engine configuration and any aftermarket modifications. If you're having trouble locating it, a visual inspection of the area near the radiator and hoses should help. You can also consult your owner's manual or a repair manual for a diagram.