My coolant is Brown after one day..

The heater core is inside your cab the hot coolant flows through to give you heat after years they can start to leak

 

I understand what the heater core does.I don't see any leaks

 

Time to break out your pressure tester if in fact the coolant is leaking

 

I will do this.Im guessing it's my heater core

 

I looked at it when it was running today and it actually was visably leaking right around the top of the bottom radiator hose.Im guessing thermostat

 

^^^^