If it were the water pump, the car would run hot. Top off your coolant/antifreeze. Large reservoir, top right corner under the bonnet. You're the second one today that's had this issue, lol.

 

Maguar, sounds like you might have this problem (I just cross-posted it on the other thread from today).

http://consumerguideauto.howstuffworks.com/2002-to-2008-jaguar-x-type-2.htm

Coolant leak: Coolant loss from broken expansion tank bleed tube could lead to overheating. (2002-06)
[/align]
I'm surprised they have to replace the whole expansion tank. Can't they just replace the bleed tube?

 

Sounds like maybe your thermostat is stuck in the open position... is your temp guage showing the temps of the engine to be cooler than normal?

 

General heater diagnosis. First off it has been between -10 and -20 F here for the last few days, don't expect your heater to produce the same amount of heat output as if it were +20.

Make sure the system is full, heat that flucuates when you rev the engine or drive at high speeds can indicate extreme cold, or an air pocket in the system, primarily the heater core. It can also indicate a sticking open t-stat or restricted heater core. You can check the t-stat and heater corewith an infrared heat sensing gun by checking inlet and outlet temps. If you have high mileage either could be the cause though t-stats on the Xs are much more common than heater core problems.

 

Hey Real_Tech:
elsewhere in one of these threads you gave some really good tips on how to make sure your coolant is full, with no air bubbles, etc.
I would think that would make a VERY USEFUL FAQ.
Ansd I could sure use the tips myself, since I can't seem to find that thread right now.