03LexIS300

speaking from a mechanics point of view if the water pump goes out 9 times out of 10 your engine is not affected, however on a car that the water pump is driven by the timing belt if the bearings go bad it could cause the timing belt to possibly slip and jump or back off timing, or it could possibly shred the timing belt causing it to break, which would affect your engine if you engine is considered an "interferance" engine, you can buy books and manuals from dayco telling you specs on timing belts such as milage intervals to replace the belt and if your water pump is timing belt driven and if the engine is an "interferance" engine or not and drive belts and etc. the 2jz is an "interferance" engine so if the belt breaks it will wipe out the valves and possibly some pistons while its at it. however the water pump is not driven by the timing belt, so if the pump goes out and you do not check the coolant or notice the leak under your car or check your temperature guage then you will overheat the engine, which it may still run but it will slowly start to loose power and blow the head gasket and basically cook the motot, then the motor will be toast and you need a new one, another possible scenario is the water pump leaks and the bearings go bad and puts a side load on the drive belt and breaks it. honestly as long as you check your coolant regularly you will be fine. so if your water pump goes out on the is300 worst case scenario is some time, water pump, coolant, drive belt, and possibly a dead battery depending on how much you run it after or if the drive belt breaks. best case scenario some time, water pump, and coolant