Replacing Miata Small Coolant Hoses: A Step-by-Step Guide Using Long Nose Hose Clamp Pliers

Replacing the small coolant hoses on a 1.8L NA Miata can be a fiddly job, especially the ones tucked away under the intake manifold. While it might seem daunting, with the right tools and a bit of patience, it’s a task you can tackle yourself. This guide will walk you through the process, focusing on using long nose hose clamp pliers to access those hard-to-reach spring clamps and get the job done efficiently.

Before we begin, let’s identify the hoses we’ll be replacing:

• Hose A – Connects the back of the engine to the oil cooler (Part Number: BPE8-15-536)
• Hose B – Runs from the oil cooler to the throttle body (Part Number: BPE8-13-681)
• Hose C – Goes from the throttle body to the thermostat housing (Part Number: BPE8-13-682)
• Bypass Hose – (Part Number: B61P-15-261A)

Having these names and locations clear will make the process smoother.

Essential Tools for Hose Replacement

Besides your standard set of automotive tools, a couple of specialized pliers will be your best friends for this job:

• 4-inch Micro Locking Pliers (Vice Grip type): Ideal for maneuvering in very tight spots.
• 8-inch Long Nose Locking Pliers: Crucial for reaching and manipulating spring clamps in confined areas. These long nose hose clamp pliers are specifically designed for removing and installing hose clamps where access is limited.

A rubber lubricant, like Simple Green or silicone spray, can also be helpful for easing the hoses onto the metal pipes.

Step-by-Step Hose Replacement Procedure

Preparation is Key:

1. Verify Hose Compatibility: Before starting, compare the new hoses you have with diagrams online or from a Mazda parts site to ensure they are correct for your Miata model. Mistakes happen, and incorrect hoses can cause headaches later.
2. Safety First: Make sure the engine is cool before you begin working on the coolant system.
3. Drain Coolant: Drain the radiator to reduce coolant spillage when disconnecting hoses.
4. Clean Work Area: Clean any dirt and grime around the oil cooler and surrounding areas, especially if you’ll be working with the oil filter removed. This prevents debris from entering the engine.

Replacing Hose A (Engine to Oil Cooler):

1. Gain Access: Create some working space by disconnecting the rubber vacuum hose from the intake manifold to the brake booster line.
2. Wiring Bundle: Locate the nut holding the wiring bundle clamp near the EGR valve and inlet pipe and remove it to move the wiring aside.
3. Protect Yourself: Identify the sharp corner on the bracket where the hard clutch pipe meets the rubber clutch hose. File down this sharp edge to prevent cuts on your arm. Apply duct tape for extra protection.
4. Clamp Access and Removal: Locate the spring clamp on Hose A. Apply lubricant to the clamp area. Use your long nose locking pliers to compress the spring clamp. Slide the clamp back along the hose, away from the metal pipe.
5. Hose Removal: Carefully cut the old Hose A and detach it from the metal pipe.
6. New Hose Installation: Compare the new Hose A with the old one to ensure correct orientation. Place the spring clamp onto the dry new Hose A, keeping the locking pliers engaged on the clamp. Push the new hose onto the metal pipe until it’s fully seated.
7. Clamp Placement: Apply lubricant to the hose end and slide the spring clamp into its correct position over the connection. Release the locking pliers.
8. Reassemble: Reconnect the vacuum hose and secure the wiring bundle clamp nut.

Replacing Hose A (Oil Cooler Side) and Hose B (Oil Cooler to Throttle Body):

1. Raise Vehicle: Loosen the lug nuts on the passenger’s side front wheel. Safely raise the front of your Miata and secure it on jack stands.
2. Remove Under Tray and Brace: Remove the large plastic undertray (held by approximately 11 fasteners) for under-car access. Remove the intake manifold brace (3 bolts).
3. Remove Wheel: Take off the passenger’s side front wheel to access the oil cooler area.
4. Final Cleaning and Oil Filter Prep: Give the oil cooler area a final cleaning. Remove the oil filter. Be prepared for oil spillage and use plastic bags and rags to mask and protect the area.
5. Hose A (Oil Cooler Side) Removal and Installation: Lubricate the end of old Hose A at the oil cooler. Use your long nose locking pliers to compress the clamp and slide it back. Cut and remove the old hose. Install the new Hose A onto the oil cooler pipe, moving the clamp onto the new hose as described before.
6. Hose B (Oil Cooler Side) Removal and Installation: Repeat the process for Hose B where it connects to the oil cooler, using your long nose hose clamp pliers to manage the spring clamp.
7. Oil Filter Reinstallation: Remove the protective masking. Install a new oil filter. It’s best practice to replace the oil filter whenever it’s been removed, as the old one might not reseal properly.
8. Reassemble Under Car: Reinstall the intake manifold brace (optional, but recommended). Reinstall the road wheel, lower the car, and torque the wheel lug nuts.

Replacing Hose C (Throttle Body to Thermostat Housing) and Hose B (Throttle Body Side):

1. Upper Engine Access: Back under the hood, remove the plastic air cross tube between the throttle body and the airflow sensor. Also, remove the rubber air tube connected to the bottom of the throttle body.
2. Throttle Body Electricals: Disconnect the two electrical connectors to the throttle body and move the wiring bundle out of your way.
3. Hose C (Throttle Body Side) Access: Removing Hose C from the throttle body first will give you better access to Hose B at the throttle body.
4. Hose B (Throttle Body Side) Removal and Installation: Now that you have more space, remove the end of old Hose B from the throttle body using your long nose hose clamp pliers. Move the clamp to the new Hose B and install it onto the throttle body.
5. Hose C Installation: Install the new Hose C onto the throttle body and then connect the other end to the pipe at the thermostat housing. The long nose pliers can be helpful here as well if space is tight.
6. Reconnect Electricals: Reconnect the electrical connectors to the throttle body.

Replacing the Bypass Hose:

1. Belt Removal: To get better access to the Bypass Hose, you’ll need to remove the power steering and air conditioning fan belt. Note or photograph the belt routing before removal for easy reinstallation.
2. Bypass Hose Replacement: With the belt out of the way, you should have clear access to remove the old Bypass Hose and install the new one. Use your long nose hose clamp pliers if needed for the clamps.

Final Steps:

1. Belt Reinstallation: Replace and tension the power steering and A/C fan belt according to your Miata’s specifications.
2. Air Intake Reassembly: Reinstall the rubber and plastic air tubes from the airflow sensor to the throttle body.
3. Refill Coolant: Unless you are also replacing the radiator and heater hoses, refill the radiator with coolant to the correct level.
4. Burp the System: Run the engine to operating temperature and “burp” the air out of the cooling system. Monitor coolant levels and add more coolant as needed to ensure there are no air pockets.

By following these steps and utilizing long nose hose clamp pliers, replacing those small, hard-to-reach coolant hoses on your Miata becomes a manageable DIY task. Remember to take your time, double-check connections, and prioritize safety throughout the process.