Aisin THT-021 Engine Coolant Thermostat

Aisin Engine Coolant Thermostat for Lexus and Toyota

The Aisin THT-021 engine coolant thermostat is an Original Equipment Manufacturer part built for exact form, fit, and function. It is an OE-manufactured replacement for cooling system service on select Lexus RX450h, Lexus RX450hL, Lexus TX550h+, and Toyota Highlander applications.

Key Features

• OE-manufactured thermostat and housing assembly for precise fitment
• Includes gasket for a complete thermostat housing service
• 82°C (180°F) OE temperature thermostat specification
• Direct replacement for select Lexus and Toyota hybrid cooling systems
• Aisin THT-021 cross-references Beck/Arnley 143-0953 and Motorad 1040-180

Product Details

Aisin Original Equipment Manufacturer parts are built to match the factory design used in the vehicle’s cooling system. This thermostat assembly is specified for exact form, fit, and function, making it a direct replacement choice for drivers servicing the engine coolant thermostat on Lexus RX450h, Lexus RX450hL, Lexus TX550h+, and Toyota Highlander models listed in the fitment data. The Aisin THT-021 is designed around an 82°C operating temperature and is intended for applications that require an integral thermostat and housing design.

Compatible fitment includes 2025 Lexus TX550h+, 2020-2022 Lexus RX450h, 2020-2022 Lexus RX450hL, 2017-2019 Lexus RX450h, 2018-2019 Lexus RX450hL, 2017-2019 Toyota Highlander, and 2016 Lexus RX450h. The Aisin THT-021 is a practical OE-style replacement when servicing a thermostat housing on these vehicles.

Common Cooling System Issues Addressed

• Engine running too cool or too warm due to thermostat wear
• Coolant temperature control problems in hybrid cooling systems
• Leaks at the thermostat housing or gasket sealing surface
• Temperature fluctuation caused by a sticking thermostat
• Cooling system service needs on Lexus RX450h and Toyota Highlander models

Installation Notes and Tips

Verify engine code, cooling system configuration, and OE temperature specification before installation. Inspect the mating surfaces carefully and replace coolant according to the vehicle service procedure after thermostat housing replacement. Confirm the part number THT-021 against the VIN-based catalog listing for the exact application.

Quality Assurance

This Aisin thermostat is manufactured to OE standards for exact form, fit, and function. Aisin’s Original Equipment Manufacturer background supports factory-level application matching for the listed Lexus and Toyota vehicles.