Replacement RL31800001 Engine Coolant Thermostat and Housing Assembly

The Replacement RL31800001 is an aftermarket engine coolant thermostat and housing assembly designed as a direct-fit OEM replacement. This unit replaces Lexus/Toyota OEM part number 16031-31020 (1603131020) and restores proper engine temperature regulation to the cooling system.

The engine coolant thermostat plays a critical role in engine health by controlling the flow of coolant between the engine and radiator. It brings the engine up to its optimal operating temperature as quickly as possible, then maintains that temperature throughout operation. A faulty thermostat can cause engine overheating, prolonged warm-up times, erratic temperature gauge readings, or coolant leaks around the housing.

Key Features:

• Direct OEM replacement — matches original factory fit and function
• Thermostat opening temperature: 180°F (82°C)
• Includes thermostat and housing assembly with gasket
• Three-bolt mounting flange for secure installation
• Replaces OEM part number: 16031-31020 / 1603131020
• Cross-reference part numbers: 143-0879, 1430879, THT-004, 902-5137
• Constructed to withstand high temperatures, vibration, and chemical exposure

This thermostat and housing assembly is a reliable, cost-effective alternative to dealer-sourced OEM parts, offering equivalent fit and performance at a fraction of the cost.