Hi Guys, it seems the coolent expansion tank is a common problem. Recently I had my cooling system upgraded with new water pump, radiator, hoses. I started noticing I was loosing coolent. I have been topping up for a while and now it is mostly just water circulating so my temp is now up to 105 deg c instead of 90 deg C. I have a e53 2005 4.4i v8. Anyway, I have on many occassions put more water then what they say. I can now see signs of the coolent expansion tank or the pressure cap leaking. I assume the extra pressure should release the water somewhere (through the cap?). But, perhaps I have 1) damaged the coolent expansion tank; 2) created air pockets in the heater control valve (causing the inside cabin heating not to work); 3)caused a problem with the auxillary coolent pump.