2002 Grang Cherokee Coolant Keeps Dissapearing

My coolant in my 2002 Grang Cherokee, 101,000 Miles, 4.0L keeps dissapearing with no noticable leak or coolant on the ground. About every 1500 miles I have to top off my resevoir.

I do smell coolant when I turn on the heat/defrost and the defrost heats up well but doesn't seem to remove the fog.

I haven't taken it in but the service department at the dealer says it sounds like I need a new water pump.

Is this it?

If so, I was told it's a piece of cake to do myself. Most places want about $400 to do this.

Any help would be appreciated.