Originally Posted by jzwu
I think you are talking about the serpentine belt?
Well you think wrong.
The water pump in the Lexus 4.3L engine is driven by the timing belt (not a serpentine belt like on many cars, including my 4.4L BMW engine).
This is why if you look at any Lexus parts supply house or ebay you will see many kits for sale which include a timing belt, idler pulley, tensioner and water pump.
Get a quote sometime to replace just your water pump and you will see that to change out your water pump you must remove the timing belt. It will be very close to the cost of replacing your timing belt because the normal timing belt service includes a new water pump and the other ancillary parts, and the timing belt itself can be had for between $25 and $50.
This is also why it is very
important to renew your coolant every couple of years to keep the water pump happy (read well lubricated). If the water pump seizes it will cause the belt to break and your valves (timing uncontrolled) will get cozy with your piston heads (to the tune of $5K-$6K in repairs).