Antifreeze fill on a 4.7

[lilrez]

Wifes new/used 03 Dakota 4.7 liter. Comes home tells me truck was getting hot. Checked Coolant resivor and filled it, then opened cap and filled righ to the top. Approx 4 liters was added. Couple weeks later checked cap again, and toped up another 2 liters. I cant see a leak below the truck, and exhaust does not smell extremly sweet.
I do not have a manual for the truck. Should the coolant be added at the cap, or am i adding too much and is it blowing the exess out on the road as she drives away?

[peg leg]

have a radiator shop put a pressure tester on the fill cap of the radiator. They pump it to a pressure and observe whether or not the pressure stays where they set it.
Any overflow should be captured by the plastic overflow tank, so I doubt it's going anywhere but out the exhaust. It could have been improperly refilled before you bought it, and it has never "burped" properly.

[JVMopar]

Have your cooling system pressure tested.

When I fill a cooling system that has been low I always fill the overflow to the "Hot" line after fully filling and burping the air from the rest of the system.