Replacing the timing belt and the water pump at the same time is highly recommended, and on this particular vehicle we would expect it to cost around £600 to £800 with a reputable independent garage or specialist, while a main dealer would likely cost more than this again. Part of this is due to the fact that the RX400h has a relatively large V6 engine and accessing the timing belt and water pump requires significant disassembly of the engine in order to gain access, which increases the amount of labour required.