Should I change the water pump based on time/milage or wait for a problem?

No. 175,000 miles and running very well.

yes, i understand it's running very well.BUT,the timing belt should be changed every 90,000 miles under normal driving conditions and every 60,000 miles in dusty conditions! so the timing belt should have been replaced at least TWO times during the 175,000 mile period.you don't want the timing belt to break!! when changing the timing belt,it is recommended to change the water pump while doing the belt because the Water pump is driven by the timing belt. It is recommended that you consider changing the water pump when replacing the belt and related components.that Toyota engine is a very good engine and should last you a very long time,if serviced regularly.

copy all. Thanks you.

10-4,roger that!!