If the fan blade tips of a water pump mounted fan move between one-eighth and one-quarter inch back and forth, what does this indicate?

The indication of fan blade tip movement between one-eighth and one-quarter inch suggests that there is excessive play or movement in the fan assembly, which is typically a sign of a badly worn water pump bearing.

In normal operation, a properly functioning water pump should have minimal to no lateral movement, as tight bearings maintain the precise alignment necessary for optimal performance. When the bearings wear down, they can no longer keep the correct spacing, leading to excessive play in the fan blade, resulting in the observed back-and-forth motion.

Understanding the condition of the water pump can help indicate the overall health of the cooling system, as a malfunctioning pump due to bad bearings can disrupt coolant flow and lead to overheating, making this assessment critical for maintenance and repairs.