Keep coolant moving at the right temperature with the AISIN Engine Coolant Thermostat & Housing Assembly (THT-021). It drops in as a direct-fit replacement for many vehicles, among them the 2017-2019 Toyota Highlander 3.5L, 2025 Lexus TX550H+ 3.5L and 2016-2022 Lexus RX450h 3.5L; see the "Vehicles it fits" section for the full list.
A coolant thermostat regulates the flow of coolant between the engine and radiator, staying closed during warm-up and opening as the engine reaches operating temperature to help hold coolant within its intended range. This assembly combines the thermostat with its housing in one unit.
- OE engineered and manufactured: built for exact form, fit, and function as a direct replacement.
- Exact temperature: calibrated to open at the specified temperature to maintain cooling system performance.
- Temperature management: designed to keep coolant within the optimal temperature range.
- Country of origin: Japan.
Signs the original thermostat may need replacing include overheating, slow warm-up, a temperature gauge that runs low or erratically, or coolant seepage at the housing. Diagnose the cause before replacing, since these symptoms can have other sources.
Interchange: 1601-684289 · 143-0953 · 905-5212 · 1040-180 · 16031-31040
1601684289 · 1430953 · 9055212 · 1040180 · 1603131040 · 86321
Product information is for general reference and may contain errors. See our Disclaimer.
This part cross-references / interchanges with the following part numbers:
1601-684289, 143-0953, 905-5212, 86321, 1040-180, THT-021, 16031-31040
Frequently Asked Questions
What vehicles does the AISIN THT-021 fit?
It fits many vehicles, among them the 2017-2019 Toyota Highlander 3.5L, 2025 Lexus TX550H+ 3.5L and 2016-2022 Lexus RX450h 3.5L. See the "Vehicles it fits" section for the full list.
What does a coolant thermostat do?
It regulates coolant flow between the engine and radiator, staying closed during warm-up and opening as the engine reaches operating temperature to help hold coolant within its intended range.
Does this include the housing?
Yes. THT-021 is a thermostat and housing assembly, combining the thermostat with its housing in one unit.
What are signs my thermostat may need replacing?
Overheating, slow warm-up, a temperature gauge reading low or erratically, or coolant seepage at the housing. Diagnose the cause first, as these symptoms can have other sources.
Where is this part made?
The country of origin is Japan.
