What does a back and forth movement of the fan blade tips between one-eighth and one-quarter inch indicate?

A back and forth movement of the fan blade tips between one-eighth and one-quarter inch typically indicates a problem with the water pump bearing, specifically that it is badly worn. In a properly functioning water pump, the bearing should support the shaft without excessive play. When the bearing begins to wear out, it can develop lateral movement, which translates to noticeable side-to-side motion of the fan blades.

This movement is a sign of impending failure, as it suggests that the bearing is no longer maintaining the appropriate tolerances necessary for smooth operation. If left unaddressed, a worn bearing can lead to larger mechanical failures, such as overheating or complete water pump failure, which could have serious implications for engine performance and maintenance.

Normal conditions for bearings would not produce such movement, as the play should be minimal. Loose belts would affect the drive and performance of components but would not specifically cause the fan blade tips to exhibit noticeable lateral movement. A leaking fan clutch typically presents other symptoms, such as unusual noise or erratic fan operation, rather than movement of the fan blades themselves.