Chrysler Repair: heat wont work/car overheats: 01 300m, diameter hose, car overheats

Question
i have a chrysler 300m 2001 and recently couldn't get my heat to come on or it would intermittently go from hot to cold when heat is turned on, first attempt was changing the thermostat, car still overheats and no heat on the inside, next they checked the heater core, one hose was hot the other cold so we tried back flushing the heater core, car still overheated after about 30 min of running and still no heat, my local garage is now telling me it must be the water pump, I'm also told my particular car will be a chore because of where my pump is located, my question is could there be anything else causing the no heat/overheating, and how much am i looking at to change the water pump in my car, i was told probably anywhere from 400-600$,  

Answer
Hi Nicole,
I doubt it is the water pump. Before I would authorize that fishing trip I would want to be certain that the cooling system has been filled properly as it may have air trapped inside of it that impedes the flow of coolant and gives a false impression that the pump is not working. Water pumps rarely fail to pump. They fail by leaking.
So I would not authorize that pump to be changed, yet.
There is a coolant bleed valve on the lower intake manifold of the , put a 1/4 inch diameter hose that is 4 feet long on the nipple and route the hose forward and out to a can to collect any coolant discharge, in front of the vehicle (you don't want to let coolant get on the drive belts, thus the hose). You then open the bleed valve. Then you pinch close a different hose, the one that connects the two sides of the pressure bottle where fluid is added to the system. Then you add coolant in a small stream to the filler opening (so as to allow air to escape while you are pouring (or use a special funnel that is sectioned to be sure that air can escape, part no. 8195 Miller tool). You keep adding fluid to the bottle until fluid comes in a steady flow out the 4' hose. Then you close the bleeder valve. Then you keep adding fluid to the bottle until it is full on the section of the bottle that is in-board. Then you put the cap on the bottle and unpinch the hose that was previously pinched. Check that you only have coolant in the smaller in-board side of the filler bottle. If necessary drain the larger out-board side of the filler bottle by disconnecting the connecting hose and drain it from that larger side.
If that is done properly I believe you will have heat and the engine will not overheat. This is not 'rocket science' but whoever is working on the vehicle needs to know how to properly refill the system.
If the shop doesn't know this procedure show them this answer or go to a competent radiator shop where they should be aware of it.
Roland
PS Please 'rate' my answer. Thanks