Help keep your engine running at its designed operating temperature with the AISIN Engine Coolant Thermostat THK009. OE-manufactured for exact form, fit and function, it is a direct-fit replacement for many vehicles, among them the 1999-2004 Hyundai Sonata 2.4L, 2001-2005 Kia Optima 2.4L and 2001-2006 Hyundai Santa Fe 2.4L — see the "Vehicles it fits" section for the full list.
The thermostat regulates coolant flow based on engine temperature: it stays closed while the engine warms up, then opens once the coolant reaches the set point to let it circulate to the radiator and hold the cooling system in its optimal range. This unit starts to open at 82°C (179.6°F).
- OE-engineered assembly: built as an exact replacement at the exact opening temperature to maintain cooling-system performance.
- Brass and stainless steel construction: the assembly is made from brass and stainless steel.
- Jiggle pin check valve included: vents trapped air from the housing during refill to help prevent air pockets.
- Standard design; a gasket or seal is not included — consult the vehicle service information for the correct sealing components.
Signs the original thermostat may need replacing include the engine overheating (stuck closed), running cold or weak cabin heat (stuck open), or temperature-related warning codes. Country of origin: Japan.
Interchange: 310-0012 · 143-0722 · 25500-38001 · 545-180 · A2413-82G
3100012 · 1430722 · 2550038001 · 545180 · A241382G · 33996 · 48268
This part cross-references / interchanges with the following part numbers:
310-0012, 143-0722, 33996, 2550038001, 25500-38001, 545-180, THK-009, 48268, A2413-82G
Frequently Asked Questions
What vehicles does the AISIN THK009 thermostat fit?
It fits many vehicles, among them the 1999-2004 Hyundai Sonata 2.4L, 2001-2005 Kia Optima 2.4L and 2001-2006 Hyundai Santa Fe 2.4L. See the "Vehicles it fits" section for the full list.
At what temperature does this engine coolant thermostat open?
It starts to open at 82°C (179.6°F), holding coolant flow until the engine warms up and then opening to circulate coolant to the radiator.
Does it include a jiggle pin check valve?
Yes. The included jiggle pin check valve helps vent trapped air from the housing during a coolant refill to reduce air pockets in the system.
Is a gasket or seal included?
No, a gasket or seal is not included. Consult the vehicle service information for the correct sealing components and installation procedure.
What are the signs my thermostat may need replacing?
Common signs include the engine overheating (stuck closed), the engine running cold or weak cabin heat (stuck open), or temperature-related warning codes. Diagnose the cause before replacing.
