Subaru WRX Engine Coolant Thermostat Guide for 2012-2023 Models
Prevent overheating or running cold by understanding how to choose the right thermostat for your WRX.
- First, confirm your engine: 2012-2014 WRX models have an EJ-series engine, while 2015-2023 models have an FA-series engine. They use different thermostats.
- A stuck-closed thermostat will cause rapid overheating and can destroy your engine; pull over immediately if this happens.
- For a daily driver, an OEM-spec thermostat is the most reliable choice. Lower-temperature 'racing' thermostats can hurt performance and efficiency on a stock vehicle.
- When replacing, ensure the new thermostat's jiggle pin is installed in the 12 o'clock (up) position to allow air to bleed from the system.
A Critical Part for Your WRX's Health
The engine coolant thermostat is a vital gatekeeper for your WRX's cooling system. Its job is simple but crucial: regulate engine temperature. A failed thermostat can lead to serious problems, from poor performance and fuel economy to catastrophic engine damage from overheating. Whether it sticks open or closed, it's a problem you need to address promptly.
Important: Two Different Thermostats for 2012-2023 WRX
Before buying a new thermostat, you must identify your WRX's engine. There are two different designs for this generation range:
- 2012-2014 Subaru WRX (EJ25 Engine): These models use a thermostat that opens at approximately 172°F (78°C). The common OEM part number is 21200AA072. 🎬 See this 2008-2014 WRX thermostat replacement walkthrough
- 2015-2023 Subaru WRX (FA20F Engine): These models use a thermostat that opens at a higher temperature of approximately 190°F (88°C). The common OEM part number is 21210AA221. 🎬 Watch: How to replace the thermostat on a 2015+ WRX
Pro Tip: Always verify the part number for your specific year and model. Using the wrong temperature thermostat can negatively affect performance and fuel efficiency.
Symptoms of a Failing Thermostat
🎬 Watch: How to easily tell when your Subaru thermostat goes bad
A bad thermostat will typically fail in one of two ways: stuck open or stuck closed.
- Engine Overheating: This is the most dangerous symptom, caused by a thermostat that is stuck closed. The temperature gauge will climb into the red, especially on the highway or uphill. You might hear gurgling or boiling sounds. If you see this, pull over immediately to prevent severe engine damage.
- Engine Running Too Cold: If the thermostat is stuck open, the engine will take a very long time to warm up, or may never reach its proper operating temperature. This leads to poor fuel economy, reduced heater performance, and can trigger a Check Engine Light for code P0128.
- Erratic Temperature Gauge: The temperature gauge may swing wildly between hot and cold, indicating the thermostat is struggling to regulate coolant flow.
- Coolant Leaks: While less common, a faulty thermostat housing or gasket can cause coolant to leak near the thermostat's location, typically where the lower radiator hose meets the engine.
Known Issues, Recalls, and TSBs
There are no active recalls for the engine coolant thermostat on the 2012-2023 Subaru WRX. However, Subaru did issue a Technical Service Bulletin (TSB 09-94-22) for the 2022 WRX that addresses several Diagnostic Trouble Codes (DTCs), including P0128, which relates to the thermostat. This TSB involves a software update, but if the thermostat is mechanically stuck, it must be replaced.
Don't Confuse with the Thermo Control Valve (TCV)
Some newer Subaru models (like certain Foresters and Outbacks) use an electronic Thermo Control Valve (TCV) which has a warranty extension. The 2012-2023 WRX does not use this part; it uses a traditional, mechanical thermostat. Information about the TCV does not apply to your WRX.
Choosing the Right Aftermarket Thermostat
When replacing your thermostat, you have several options. For a daily driven WRX, sticking with an OEM-spec part is the safest bet.
Brand Quality Tiers
- OEM (Subaru Genuine): The highest quality and most reliable option. It's designed specifically for your engine and guarantees correct fitment and temperature rating. While it costs more, it provides peace of mind for a critical component.
- Performance Aftermarket (Mishimoto): Mishimoto offers 'racing' thermostats that open at a lower temperature. The theory is to begin cooling sooner, which can be beneficial for highly modified or track-driven cars. However, for a stock or daily-driven WRX, this can cause the engine to run too cool, hurting fuel economy and performance. Quality control can be inconsistent according to some user reviews.
- Standard Aftermarket (Gates, Calorstat, Motorad): These brands offer affordable, OEM-temperature replacements. Gates is a generally respected brand. Motorad is a budget option, but some users report premature failures. Given the low cost of the part and the high cost of potential engine damage, investing in a quality OEM or reputable aftermarket brand like Gates is strongly recommended over the cheapest option available.
| Part Type | Estimated Cost |
|---|---|
| New OEM | $25 - $45 |
| New Aftermarket | $15 - $70 |
| Shop Labor | $100 - $225 |
Frequently Asked Questions (FAQ)
Should I get a lower temperature 'racing' thermostat?
For most WRX owners, the answer is no. The stock engine is designed to run at the temperature set by the OEM thermostat (around 172°F for EJ engines, 190°F for FA engines). Running a cooler thermostat can prevent the engine from entering its efficient 'closed-loop' operating mode, which can increase fuel consumption and wear. Lower temp thermostats are best reserved for heavily modified or dedicated track cars that generate excessive heat.
Is replacing the thermostat a good DIY job?
Yes, for a moderately experienced DIYer. The process involves draining the coolant, removing the lower radiator hose, unbolting the housing, and swapping the part. The most critical steps are ensuring the new thermostat is installed in the correct orientation (jiggle pin up) and properly bleeding all air from the cooling system afterward to prevent overheating.
Why is OEM recommended so often for this part?
The thermostat is a low-cost part that plays a high-stakes role in protecting your engine. While many aftermarket parts are excellent, the thermostat is one area where the guaranteed fit, correct temperature rating, and reliability of the OEM part provide significant peace of mind against the risk of catastrophic engine failure from overheating.
What is the 'jiggle pin' and why is it important?
The jiggle pin is a small metal pin in a hole on the flange of the thermostat. It allows a small amount of air and coolant to pass through even when the thermostat is closed. This is critical for bleeding air out of the cooling system during a refill. It must be installed in the 'up' or 12 o'clock position to work effectively.
Helpful Videos
Technical Specifications
OEM Part Numbers: 21200AA072 (For 2012-2014 WRX) 21210AA221 (For 2015-2023 WRX)
2012-2014 (EJ25): 172°F / 78°C opening temp. 2015-2023 (FA20F): 190°F / 88°C opening temp.
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Subaru WRX:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- A Critical Part for Your WRX's Health
- Important: Two Different Thermostats for 2012-2023 WRX
- Symptoms of a Failing Thermostat
- Known Issues, Recalls, and TSBs
- Don't Confuse with the Thermo Control Valve (TCV)
- Choosing the Right Aftermarket Thermostat
- Brand Quality Tiers
- Frequently Asked Questions (FAQ)
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