21200AA170 Subaru THERMO ASSY, Price: 14.15$, Weight: 0.123kg

Engine Coolant Thermostat Assembly for Subaru Boxer Engines

This precision coolant thermostat keeps your engine at the correct operating temperature, so it warms up fast and stays stable under load. Proper heat control means better fuel economy, smoother drive, stronger cabin heat, and longer engine life. Built with a wax-charge capsule, robust spring, and tight sealing ring, it delivers OEM-level fit and durability for daily use and tough climates.

Why this part is needed ❄️

Without a healthy thermostat, the ECU and cooling system cannot balance heat. This part controls when coolant flows to the radiator, protecting the head gaskets and maintaining ideal performance in traffic, highway, or off-road conditions.

How it works

Cold start: valve stays closed, coolant circulates inside the block for quick warm-up. As temperature rises, the wax pellet expands and the valve opens progressively, routing coolant through the radiator. The design stabilizes temperature and supports proper fan and heater operation.

What happens if it fails

Stuck closed: rapid overheating, boiling coolant, possible head warpage. Stuck open: engine runs cold, rich fuel mix, poor MPG, weak heater, possible P0128 code. Leaks or weak spring cause temperature swings and air pockets.

Compatibility

• Legacy
• Forester
• Impreza