Infiniti Fx35 Thermostat Location and Replacement Guide

The Infiniti FX35 uses a 3.5L V6 engine, and the thermostat is part of the cooling system that regulates engine temperature. Locating the thermostat is essential for inspection, replacement, or troubleshooting cooling issues such as overheating, temperature fluctuations, or thermostat sticking. This guide outlines where the FX35 thermostat sits, how to identify the thermostat housing, and practical steps for inspection and replacement. It focuses on common layouts for the model years that used the VQ35DE engine and provides safe, careful instructions for DIY maintenance.

Where The Thermostat Is Typically Located In The FX35

The thermostat in the Infiniti FX35 is housed inside the thermostat housing, which is attached to the engine where the upper radiator hose connects. In most FX35 models, this housing is located on the passenger side of the engine bay, near the intake manifold and between the radiator and the engine block. The housing is usually a metal or plastic component with a removable cap or cover secured by bolts. The upper radiator hose will connect directly to this housing, making it the primary clue for locating the thermostat.

Key indicators you’ve found the thermostat housing include:

• Accessible bolts: A small set of bolts or screws around a cap or flange.
• Hose connections: One large hose (typically the upper radiator hose) and a smaller heater hose connected to the housing.
• Thermal cap: A removable cover that hides the thermostat inside the housing.

Tools You May Need

• Socket set with metric sizes
• Torque wrench
• Flat-head and Phillips screwdrivers
• Gasket scraper or plastic putty knife
• New thermostat and gasket or O-ring
• Coolant compatible with the FX35 (check owner’s manual)
• Drain pan and coolant fill funnel
• Safety gear: gloves and eye protection

Preparation And Safety

Before beginning any work, ensure the engine is cool to avoid burns from hot coolant. Disconnect the negative battery terminal to prevent accidental starts. Place the vehicle on a level surface with the parking brake engaged. Have a clean drain pan ready to catch coolant during the cooling system drainage. If you’re unsure about the process, consult a service manual or a professional technician for proper guidance.

Inspecting The Thermostat And Housing

Inspection helps determine whether replacement is needed or if the issue lies elsewhere in the cooling system. Steps include:

• Locate the thermostat housing as described above.
• Inspect for coolant leaks around the housing bolts and gasket interface.
• Check the thermostat cap for wear or damage; a cracked cap can affect sealing and pressure.
• Gently remove the housing cap to expose the thermostat. Observe if the thermostat moves freely and if the flow path is unobstructed.
• Test for proper operation by placing the thermostat in hot water to verify it opens within the manufacturer’s specified temperature range (refer to the service manual).

Replacing The Thermostat

Replacing the thermostat in the FX35 can prevent overheating and improve cooling system efficiency. Follow these steps carefully:

1. Drain coolant from the radiator to a level below the thermostat housing to minimize spillover.
2. Remove the bolts or fasteners securing the thermostat housing. Carefully lift the housing away to access the thermostat inside.
3. Carefully remove the old thermostat and gasket or O-ring. Note the orientation of the thermostat for proper reinstallation.
4. Clean the mating surfaces on the housing and engine block with a gasket scraper or plastic tool to avoid any debris interfering with the seal.
5. Install the new thermostat in the correct orientation. The thermostat should open toward the engine as designed by the OEM. Place a new gasket or O-ring on the housing or thermostat as required by the component design.
6. Reattach the thermostat housing with bolts to the specified torque (refer to the service manual for exact values). Avoid overtightening, which can crack the housing or warp the gasket surface.
7. Refill the cooling system with the appropriate coolant. Bleed air from the system if required by the FX35 cooling system procedure to prevent air pockets.
8. Reconnect the battery, start the engine, and monitor the temperature gauge. Check for leaks around the housing and ensure the heater produces warm air once the engine reaches operating temperature.

Tips For Diagnosing Thermostat-Related Issues

• Overheating in traffic: Could indicate a thermostat that sticks closed or insufficient coolant flow.
• Erratic temperature gauge readings: May signal air pockets, a faulty temperature sensor, or a partially obstructed cooling path.
• Coolant loss without visible leaks: Could point to a gasket issue or a small leak at the thermostat housing.
• Slow warm-up: Often tied to thermostat remaining closed longer than normal or air in the cooling system.

Common Pitfalls And How To Avoid Them

Some mistakes DIY enthusiasts commonly make include over-tightening the thermostat housing bolts, using the wrong coolant type, or failing to properly bleed air from the cooling system. Always follow the manufacturer’s torque specs, use the recommended coolant, and perform a thorough coolant bleed to prevent air pockets that can cause overheating or cold spots in the heater core.

When To Seek Professional Help

If there are persistent cooling issues after replacing the thermostat, or if there are leaks, warped housings, or signs of overheating that don’t resolve with a thermostat replacement, consult a certified mechanic. The FX35’s cooling system interacts with several components, including the radiator, water pump, and radiator fans, which may also require inspection.

Additional Resources

• Infiniti service manuals and factory diagrams for the VQ35DE engine
• OEM thermostat and gasket part numbers specific to FX35 model years
• Guides and videos from reputable automotive repair sites focusing on the FX35 thermostat replacement