iBuildRacecars Cylinder 4 Cooling Connection Subaru WRX 2002-2014 / STI 2004-2021

This kit is designed to help increase the cooling to the #4 cylinder on the Subaru EJ series engines. This hose kit connects to an existing port on the back of the left-hand side of the motor that is blocked off from the factory with a plug.

We even included the right tool to get the job done!

Compatibility: 

All Subaru EJ Series Motors

Included in the kit:

• 10 Inches of Gates Engine Coolant Hose
• -10 AN 45 Degree Push To Connect Fitting
• -10 AN to Metric Straight Thread Adapter
• Aluminum Crush Washer for Metric Straight Thread Connection
• 304 Stainless Steel 5/8” Barbed Tee Connection
• Qty 4 Stainless Steel Hose Clamps
• 12mm Allen Socket with 1/2” Square Drive

Basic Installation Steps:

• Drain coolant from the engine below the level of the plug on the back of the engine
• Remove the factory coolant plug using the supplied 12mm allen socket
• Install straight thread to 10AN adapter with included aluminum crush washer
• Test fit 10AN 45-degree fitting with the hose attached
• Locate the heater core hose that connects to the firewall and mark where to cut and install the stainless tee fitting
• Trim included Gates heater hose (different chassis and models require slightly different hose lengths)
• Install tee connector inline with existing heater hose with the center connection being used for the provided line, use hose clamps on all 4 barbed hose connections
• Tighten the 10AN connection, ensure the new hose does not rub on any other parts in the engine bay paying close attention to the steering shaft

• Refill coolant and properly “burp” the system to remove all air introduced during the installation

*Note: If you see corrosion or surface imperfections on the sealing face of the block you can apply Permatex or similar sealing material to the metric straight threads on the adapter fitting into the block for a secondary sealing point. NEVER apply any type of sealant or tape to the threads on AN fittings.

This is a universal kit, depending on the year and chassis this is being installed on the length of the heater hose and the point at which you connect into the factory hoses will be slightly different. We will be posting more detailed instructions and photos for each unique application very soon.

The intent of this kit is to solve an imbalance in the factory cooling system on the EJ series motors. Subaru designed the cooling system to ensure that cylinder #4 ran slightly hotter than the rest of the cylinders, this allowed them to then tune the system so that if a knock were to occur it would happen first on cylinder #4. While this simplifies the control system on a factory car it doesn’t allow tuners to get the most potential out of the engines, the tune is basically limited by an intentional design flaw in the cooling system. Since this type of modification (not just our kit) can affect the knock response on your engine we recommend consulting with your tuner before installation and having your tuner review logs after installation. Professional installation is recommended.