On the 617 diesel engines, there is a water bypass line from the cylinder head to the water pump (the small crescent shaped metal tubular one). It is listed in the CD as a “vent line” which should actually answer my own question, but it appears from the cooling system diagram that the venting of air occurs elsewhere. Which leads back to the question – what is the purpose of this line?

Has anyone ever had this line get plugged up on them, and what were the symptoms or consequences?

Thanks Everyone!