That is the water pump pulley.
Pulley.
The belt on a 2000 Ram uses a spring loaded tensioner pulley. It self tightens.
Gas engine, it is the part the fan is screwed onto. Diesel, it is just to the passenger side nd down from the fan pulley.
That pulley is part of the water pump. The water pump has failed and needs replaced.
You need a 36 mm wrench and a spanner to hold the pulley. Turn counter clockwise to loosen.
loosen the idler pulley and then remove the belt. then you remove the fan shroud i believe its like 4 bolts, then you remove the fan. after that you can remove the water pump.
You need two special tools, A 36mm wrench and a spanner to hold the pulley still. While holding pulley yo use 36mm wrench and a hammer to turn fan nut counter clockwise.
12 valve it is on the front of the engine, above the crankshaft pulley. 24 valve it is behind the starter, in the side of the block.
You can remove the old serpentine belt on your 2004 Dodge Ram by loosening the tensioner pulley. Put the new serpentine belt on and tighten it with the tensioner pulley.
I have a 1995 Dodge Ram 1500 and it has a counter-clockwise rotation; or a left turn rotation.
Check clutch fan
Right front of engine block (next to the fan pully) It is the smooth round pulley that is about 3 inches across.