Scion tC Engine Coolant Thermostat Replacement Guide (2005-2016)
Learn how to choose the right engine coolant thermostat to fix overheating or running-cold issues on your 2005-2016 Scion tC.
- The most common failure is 'stuck open', which causes the engine to run cold and triggers a P0128 code.
- For a stock Scion tC, always choose a thermostat with the OEM temperature rating (180°F/82°C).
- Aisin is an OEM supplier to Toyota/Scion, making it a top-tier choice for aftermarket replacement.
- Always replace the thermostat gasket, which is often sold separately, to prevent coolant leaks.
Is Your Scion tC Thermostat Failing?
A failing thermostat in your Scion tC can cause frustrating problems. It typically fails in one of two ways: stuck open or stuck closed. A thermostat stuck closed is serious, as it will cause the engine to quickly overheat, potentially leading to severe engine damage. More commonly, especially on the Scion tC, the thermostat fails by getting stuck open. This prevents the engine from reaching its proper operating temperature.
Key Symptoms of a Bad Thermostat
- Check Engine Light: A thermostat stuck open will often trigger the diagnostic trouble code P0128 (Coolant Temperature Below Thermostat Regulating Temperature).
- Engine Overheating: If the thermostat is stuck closed, the temperature gauge will climb into the red very quickly after starting the engine.
- Engine Running Cold: If stuck open, the temperature gauge will take a very long time to reach the middle, or it may drop towards cold when you are driving at highway speeds.
- Poor Heater Performance: The cabin heater uses hot coolant to warm the air. If the engine isn't getting hot enough, you'll get lukewarm or cold air from your vents.
- Decreased Fuel Economy: An engine that runs too cold is not efficient, which can lead to using more fuel.
Generation Differences
The 2005-2016 Scion tC spans two generations with different engines: the 1st Gen (2005-2010) uses the 2.4L 2AZ-FE, and the 2nd Gen 🎬 Watch this step-by-step thermostat replacement for first-generation models. (2011-2016) uses the 2.5L 2AR-FE. While the function is the same, the exact thermostat part number is different. Always confirm the part fits 🎬 See how to fix a P0128 code on 2011-2016 models. your specific year and engine.
Choosing the Right Aftermarket Thermostat
For a daily-driven Scion tC, using a thermostat with the factory-specified temperature is essential for proper engine management. Aftermarket quality can be excellent, sometimes even coming from the same factory as the original part.
Brand Quality Tiers
- OEM-Equivalent (Best Choice): Brands like Aisin are often the original equipment manufacturer for Toyota and Scion. Choosing Aisin is the closest you can get to buying the part from a Toyota dealer, ensuring perfect fit and correct temperature rating. Beck Arnley also focuses on sourcing parts that match OEM specifications.
- Trusted Aftermarket (Good Choice): Brands like Gates and Motorad are well-known in the cooling system world and produce reliable, standard-temperature replacement thermostats that meet or exceed OEM standards.
- Performance (Special Use): A brand like Mishimoto offers a “low-temperature” racing thermostat that opens earlier (around 155°F instead of 180°F). This is not recommended for a stock, daily-driven vehicle. It is designed for heavily modified or track-use cars and can cause the check engine light to come on (P0128) and reduce efficiency in normal driving.
Don't Forget the Gasket!
The thermostat requires a rubber gasket or seal. This part is critical for preventing leaks but is often sold separately. Do not reuse the old gasket; always install a new one with your new thermostat.
Cost of Replacing a Scion tC Thermostat
Replacing the thermostat is a relatively affordable repair. The parts are inexpensive, and the labor is not excessive.
| Part or Service | Estimated Cost |
|---|---|
| New Aftermarket Thermostat | $17 - $70 |
| New OEM Thermostat | $22 - $40 |
| Shop Labor | $100 - $200 |
| Total Estimated Cost | $120 - $270 |
Frequently Asked Questions
Is replacing the thermostat a DIY job?
Yes, for someone with basic mechanical skills and tools. The thermostat is located behind a housing connected to the lower radiator hose. Access can be tight, especially for the lower of the two 10mm nuts holding the housing. The biggest challenges are draining the coolant without a mess and properly bleeding the air out of the system 🎬 Follow this guide to properly bleed your cooling system. afterward.
Are there any recalls on the Scion tC thermostat?
No, there are no active recalls or common Technical Service Bulletins (TSBs) from Scion or the NHTSA specifically for engine thermostat failure on the 2005-2016 Scion tC.
What temperature thermostat should I buy for my Scion tC?
For a stock vehicle, you must use a thermostat with the OEM-specified temperature, which is typically 180°F (82°C). Using a lower temperature thermostat can cause check engine lights and poor performance.
What coolant should I use for my Scion tC?
It is highly recommended to use Toyota Super Long Life Coolant (pink). This is the specific type of coolant designed for your vehicle's cooling system. Using the wrong coolant can lead to premature wear and damage to cooling system components.
Helpful Videos
Technical Specifications
OEM Part Numbers: 90916-03136 90916-A3003 90916-03129
Standard Opening Temperature: 180°F (82°C)
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.
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