1999 Chevy Suburban Fan clutch & disappearing coolent

Your lower intake gaskets are probably leaking coolant. It may be leaking inside of the engine and getting into your oil - or - leaking where it evaporates before it can be detected. Coolant in oil will destroy your engine quickly. The fan clutch on your engine rarely goes bad. But if it does the fan will not rotate of move enough air through the radiator - thus causing overheating.