Modifying the factory coolant system on Honda B-series engines to delete the stock coolant port and convert it to a threaded fitting is a common practice for custom cooling setups, turbocharger coolant lines, or to achieve a cleaner engine bay aesthetic. This procedure involves permanently altering the engine block or cylinder head, requiring careful execution to prevent damage and ensure system integrity.

Applicability#

This modification is relevant for Honda B-series engines, including the B16, B17, B18, and B20, found in models such as the Civic, CRX, Del Sol, and Integra.

Tools and Materials#

Before beginning, gather the necessary tools and materials:

• Safety glasses and gloves
• Coolant drain pan
• Shop rags or absorbent towels
• Drill and appropriate drill bits
• Tap handle and tap (specific size to be determined by desired fitting)
• Thread sealant (e.g., PTFE paste or liquid thread locker suitable for coolant systems)
• Compressed air
• Vacuum cleaner (shop vac)
• New threaded plug or fitting (e.g., NPT or AN adapter)
• Brake cleaner or similar degreaser
• Torque wrench
• Factory Service Manual (FSM) for specific drill/tap sizes and torque specifications

Procedure for Coolant Port Conversion#

1. System Preparation and Draining#

Warning

Always allow the engine to cool completely before working on the cooling system to prevent severe burns from hot coolant.

• Position the vehicle on a level surface and ensure it is securely supported.
• Place a drain pan beneath the radiator drain plug or lower radiator hose.
• Open the radiator drain plug or disconnect the lower radiator hose to completely drain the engine's coolant.
• Once drained, re-secure the drain plug or hose.

2. Identifying and Preparing the Port#

• Locate the coolant port to be modified. This is typically a pressed-in or threaded nipple on the cylinder head or engine block, often near the thermostat housing or on the intake manifold side.
• Thoroughly clean the area around the port using a degreaser to remove any oil, dirt, or coolant residue.

3. Removing the Existing Nipple (If Applicable)#

• If the port is a pressed-in nipple, carefully remove it. This may involve using a pry tool, vice grips, or a slide hammer. Exercise caution to avoid damaging the surrounding casting.
• If the port is a threaded fitting, use an appropriate wrench or socket to remove it.

4. Drilling and Tapping the Port#

Caution

Metal shavings entering the cooling system can cause significant damage to the water pump, radiator, and heater core. Extreme care must be taken to prevent this.

• Confirm Drill and Tap Sizes: Consult the desired threaded fitting's specifications and the Factory Service Manual to determine the precise drill bit size for the pilot hole and the correct tap size for the chosen thread (e.g., 1/8" NPT, 1/4" NPT).
• Protect the Engine: Before drilling, consider methods to prevent shavings from entering the engine. This can include:
• Packing the coolant passage with grease (which can be flushed out later).
• Using a shop vacuum continuously at the drilling site.
• Placing a rag or paper towel just inside the port (ensure it can be fully retrieved).
• Drilling: Using the specified drill bit, carefully drill a pilot hole into the port. Maintain a straight and perpendicular angle to the surface.
• Tapping: Apply cutting oil to the tap. Slowly and carefully begin tapping the hole. Turn the tap clockwise for a half to full turn, then counter-clockwise a quarter turn to break the chip. Repeat this process until the desired thread depth is achieved.

5. Thorough Cleaning#

Important

This step is critical. Any remaining metal shavings can cause catastrophic damage to the cooling system.

• Immediately after tapping, use a shop vacuum to remove all visible metal shavings from the area.
• Flush the coolant passage thoroughly with brake cleaner or a similar solvent. Use compressed air to blow out any remaining debris, ensuring the passage is clear.
• If grease was used to catch shavings, ensure it is completely removed by flushing with solvent and then water.

6. Installing the New Fitting or Plug#

• Apply a suitable thread sealant (e.g., PTFE paste or liquid thread locker designed for coolant systems) to the threads of the new fitting or plug.
• Carefully thread the new fitting or plug into the prepared port by hand to ensure it starts correctly.
• Using an appropriate wrench, tighten the fitting to the manufacturer's recommended torque specification. If no specific torque is available for the fitting, tighten until snug, then an additional 1/4 to 1/2 turn, ensuring not to overtighten and strip the threads.

7. Refilling and Verification#

• Refill the cooling system with the appropriate Honda-approved coolant mixture.
• Bleed the cooling system thoroughly to remove any trapped air.
• Start the engine and allow it to reach operating temperature. Carefully inspect the newly installed fitting for any signs of leaks.
• After the engine cools, recheck the coolant level and top off if necessary.

Tip

Monitor the coolant level and check for leaks over the next few driving cycles to ensure the modification is secure and leak-free.