There is a coolant line that runs down the passenger side of the engine and goes to the backside of the water pump its a rreturn line and mine is not used there is a bolt in a piece of hose hose blocking it off does anyone know what it's for

 

I'm pretty sure that is your secondary loop for the heater. It allows coolant to circulate through the heater core before the thermostat opens. Does the heat in your truck work?

 

Ueah heat works great

 

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