Checked the water pump weep hole today and I have coolant leaking out of it, so I know it needs to be changed. Will I loose all my coolant by replacing the pump or just a little bit? This would happen on a Sat. with no Cummins shops open to get more coolant. I won't put just any in it. I currently have about 1 1/2 galons in the tool box if I need it.