The Aeroflow coolant hose kit for the Subaru EJ engines was designed to increase the coolant water flow onto cylinder 4. This kit allows the coolant to travel through the cylinder 4 passage and recirculate around the cooling system. Routing the coolant from another source allows additional coolant to get to the passenger side head, this additional coolant reduces the combustion temperature, risk of premature detonation and head gasket failure. How the temperatures are balanced across both case halves. This is essential with close deck blocks due to the minimal coolant flow. The kit includes fittings, a new coolant hose with spring clamps, which you simply fit into the unused port at the back of the block at cylinder 4's location. This can then the positioned into the water matrix tee pipe directly above using the supplied fittings on the tee piece.