I have a 2001 XKR which came with the plastic impeller water pump. These can fail along with the thermostat. I found a water pump on eBay with the metal impellers for $52 in S&H (dealer wanted $450 to change this item).

1/ Loosen the 3 bolts (8mm)on the water pump pulley. Its the pulley under the top super charger pulley.
2/ Realease the main belts. Under the water pump pulley and slight towards the driver side there is a pulley with a 15mm bolt, this is the spring loaded adjust pulley turn this towards the passenger side this will give you the slack needed to remove the main belt from this pulley.
3/ Now remove the water pump pulley.
4/ Drain the coolant, passenger side at the bottom of the radiator there is a plastic plug with a cross head. Once the fluid is removed tighten the plastic plug back up and move your coolant collecting bowl under the main crank pulley, as there will still be coolant in the water pump when we release that.
5/ Undo the 5 8mm bolts on the water pump and remove the pump. You may need to leaver it out. But it should come out fairly easy. Remove slowly so as not to get coolant all over you belts.
6/ Insert new water pump and grease you gaskets. Clean all surfaces first.
7/ Replace water pump pulley and main belt. Check the belt is sitting ok on all pulleys.
8/ Refill with coolant and bleed supercharger.

Should take you about an hour if you go slow and clean everything as you go. Simple DIY job

 

Hey simon, sounds like a good DIY project and a good write up, thanks.
Just one thing though, If possible we always try to include pics ( they sometimes really do say more than a thousand words )
If you ever get around to any more projects like this, please, please try and add pics...They really help novices like me to undestand a little better

Thanks for sharing simon