Clutch Pressure Plate 1-31220147-1 / 8-94461108-0 For ISUZU 6BG1 6HE1 FORWARD — Ø300 Mm, 12 Kg, EXEDY ISC549 Equivalent, OEM-Spec

The Thermostat Housing with OEM references 5137160451 / 5-13716045-1 (and factory number 5-13716045-YH) is a verified replacement cooling system component for the ISUZU 4BD1 naturally aspirated diesel engine. It is used across the NPR, NKR, and NHR light truck platforms, as well as 4x4 Perentie applications in the Land Rover market.

This housing is the structural seat and enclosure for the engine thermostat. It serves as the channel and bracket for coolant flow, fixing the thermostat in position and connecting it to the pipe interface on the engine cylinder block, allowing the thermostat to automatically regulate coolant circulation based on temperature.

The housing is confirmed for all naturally aspirated 4BD1 versions ("4BD1 NA"). It is fitted to the front of the cylinder head and is supplied as the housing only — the thermostat and thermostat cover are not included. The unit is a brand-new OEM-specification aftermarket component, with a reference net weight of 0.6 kg, actual dimensions of 21.5 × 10 × 10 cm, and HS code 840999100.

This housing is confirmed for the naturally aspirated 4BD1 engine. Turbocharged or intercooled 4BD1 variants (where applicable) may use a different cooling circuit configuration. Confirm the engine aspiration type before ordering.

The package contains the thermostat housing only. The thermostat and thermostat cover are separately supplied and are not included unless explicitly stated. For a complete cooling system repair, order the thermostat and cover separately.

Reference data confirms that the OEM 4BD1 thermostat housing (5-13716045-1) is no longer available from ISUZU dealers — one source states "The 4BD1 part is no longer available from the dealers." This makes aftermarket supply the only practical sourcing channel for this component. Confirm availability with the supplier before committing to a repair schedule.

• Engine & Vehicle Coverage Verified: ISUZU 4BD1 naturally aspirated — confirmed by KLR (Australia) as "Thermostat housing for all Isuzu 4BD1 naturally aspirated versions including 4x4 Perenties." NPR application confirmed by Yishan factory data.
• Component Type & Function Verified: The housing is the "car thermostat seat" used to install the engine thermostat, serving as the channel and bracket for coolant flow and connecting the thermostat to the cylinder block pipe interface. Fitted to the front of the head.
• Net Weight Verified: 0.6 kg — confirmed by factory-direct data.
• Actual Dimensions Verified: 21.5 × 10 × 10 cm — confirmed by Yishan factory data across multiple language portals.
• HS Code Verified: 840999100 — confirmed by factory-direct data.
• Factory Number Verified: 5-13716045-YH — confirmed as the factory/tooling reference.
• Cross-Reference Density Verified: 5-13716045-0, 5-13716045-YH, 5137160451, and 5-13716045-1 are consistently grouped as interchangeable or related references across Yishan, Monotaro, and independent distributor catalogs.
• Discontinued OEM Status Verified: The OEM part 5-13716045-1 is no longer available from ISUZU dealers, as confirmed by a 4BD1 enthusiast and swap-community source.
• Supply & MOQ Reference: MOQ 10 pcs; supply capacity 10,000 pcs/month; 6-month warranty — confirmed by Polish distributor data.

• Material Specification NOT Explicitly Published: Accessible reference data does not state the material grade (cast iron vs. aluminum). One parts listing describes the housing functionally but does not specify material. Confirm material at inquiry if a specific grade is required. Do not assume cast iron or aluminum from adjacent 4BD1 cooling parts without supplier confirmation.

• Coolant leak at the thermostat housing joint: Visible drips, dampness, or crusty residue (white/pink coolant crust) around the housing-to-cylinder-head interface or the housing-to-pipe connection — the most direct sign of a failed gasket or a warped/corroded housing sealing surface.
• Overheating or temperature fluctuation: A housing that does not seal correctly allows coolant loss or air ingress, disrupting thermostat operation and causing temperature instability, especially under load or in hot climates.
• Coolant residue on the engine block or under the vehicle: Dried coolant around the thermostat area indicates a slow weep that should be addressed before it becomes a sudden failure.
• Visible corrosion or pitting on the housing sealing surface: The housing can corrode at the coolant passage edges, preventing the gasket from sealing even when new.
• Cracked or deformed housing: Impact damage or over-torqueing of the mounting bolts can crack the housing casting, requiring replacement.
• Thermostat not seating properly: A distorted housing cavity can prevent the thermostat from sealing, causing continuous coolant bypass and extended warm-up times.

• 4BD1 NA is the first check: This housing is confirmed for the naturally aspirated 4BD1. Confirm the engine aspiration type before ordering — turbocharged variants may use a different housing.
• Housing only — thermostat and cover are separate: This is the housing only. For a complete repair, order the thermostat and thermostat cover separately. Confirm package contents at inquiry.
• OEM is discontinued — aftermarket is the only source: The OEM part is no longer available from ISUZU dealers. This makes aftermarket supply the only practical channel. Confirm stock availability before scheduling the repair.
• Vehicle coverage: Core applications are NPR, NKR, and NHR with 4BD1 NA, plus Land Rover Perentie 4x4. Provide the VIN for final confirmation in mixed-fleet applications.

1. Confirm the required part first: Verify that the original housing is the 4BD1 NA unit and that the replacement's sealing surface, thermostat cavity, and pipe interface match the original. Confirm whether the thermostat and cover are being reused or replaced.
2. Cold engine only: Allow the engine to cool fully before opening the cooling system. Drain coolant to a level below the thermostat housing.
3. Remove the old housing: Disconnect the coolant pipe and any bypass hoses. Unbolt the housing from the front of the cylinder head. Note the orientation of the thermostat and any seals.
4. Clean the mating surface: Remove all old gasket residue and corrosion from the cylinder head face and the housing sealing surface. A clean, flat surface is essential for a leak-free seal.
5. Inspect the thermostat: Check the thermostat for correct operation. Replace if stuck open or closed. Confirm the correct temperature rating for the 4BD1 application.
6. Install the new housing with a new gasket: Seat a new gasket on the cylinder head, position the 5137160451 housing, and insert the mounting bolts.
7. Torque in sequence: Tighten the housing bolts evenly in a cross pattern to the workshop manual specification. Do not over-torque — the housing or cylinder head can distort.
8. Reconnect the pipe and refill coolant: Reconnect the coolant pipe and any bypass hoses. Refill with the correct coolant mixture and bleed the system according to the ISUZU procedure.
9. Run and verify: Start the engine, bring it to operating temperature, and check for leaks at the housing joint and pipe connection. Confirm the temperature gauge stabilizes and the heater blows hot.

• Inspect the housing joint at every coolant service or every 20,000–30,000 km — look for crusty residue or dampness.
• Replace the gasket whenever the housing is removed — gaskets are single-use compression seals.
• Flush coolant according to the manufacturer interval. Degraded coolant accelerates housing corrosion.
• Replace the housing if the sealing surface is pitted or warped — resurfacing is not recommended for this application.

• Standard packing: Neutral packaging or customer-branded packaging available. Actual dimensions: 21.5 × 10 × 10 cm.
• Package contents: 1 × Thermostat Housing. Thermostat and thermostat cover are NOT included unless explicitly stated — confirm at inquiry.
• Set options: Housing only (standard) / housing + gasket set (where available) — specify at inquiry.
• Suitable for: ISUZU NPR / NKR / NHR 4BD1 cooling system repair shops, Land Rover Perentie service providers, light commercial and 4x4 fleet maintenance departments, spare parts distributors, and export wholesalers.