300 HPDI cooling passage

[makomyday25]

Can anyone shed any light on what this cooling passage purpose is for? There is a cover at the top of the block forward of the crank with hoses leading down from that to a nipple on either side of the block below the bottom cylinders. The nipples that press into the block below the bottom cylinders are clogged. I have no symptoms but found the issue while changing out the Pressure control valve and hose. (The PCV hose is right next to one of the nipples on the starboard side of the motor)

[99yam40]

just my guess, but being on the top like that I would think it is a passage to bleed off trapped air from top of cooling system.

maybe someone knows for sure what it is for