Hi, I have a problem on my C220 CDI. The car will over heat and the blowers in the cab will blow cold, I removed the thermostat and checked flow and found out if I left the header tank cap off then the heaters in the cab would get warm. I've heard these have an auxiliary water pump and if so I believe that it is struggling to pump when the system is pressurised. If this is true does anyone know of the location of said pump? Or is there something else I could be missing. Thanks for any help.