Precision Works K Series Upper Coolant Housing & Filler Neck K20 K24A1Precision Works K Series Upper Coolant Housing with Built In Filler Neck Applications: K20A, K20A2, K20A3, K20Z1, K24A1 cylinder heads. Features: Precision CNC machined from billet 6061 aluminum Integrated filler neck with more clearance for turbo setups The filler neck is removable from the housing and can be relocated to a higher point The higher point of the cooling system and allows air pockets to easily escape during the coolant bleeding process.