A Practical Guide to the Scion xB Engine Coolant Thermostat (2004-2015)
Keep your xB's engine running at the perfect temperature by understanding, diagnosing, and replacing a faulty thermostat.
- A thermostat stuck closed will cause overheating and is an emergency; a thermostat stuck open is less urgent but hurts fuel economy.
- For reliability, choose an OEM Toyota thermostat or an OEM-equivalent brand like Aisin.
- The replacement procedure is different for 1st Gen (2004-06) and 2nd Gen (2008-15) models due to different engines.
- Always replace the gasket and properly bleed the cooling system of air after installation to prevent issues.
Is Your Scion xB Thermostat Failing?
A thermostat is a simple part, but it can cause major problems when it fails. It usually fails in one of two ways: stuck open or stuck closed.
- Stuck Open: When the thermostat is stuck open, coolant constantly flows to the radiator. This makes it take a very long time for your engine to warm up, especially in colder weather. You'll notice poor fuel economy, your heater may only blow lukewarm air, and your check engine light might come on with a code like P0128. 🎬 Watch: EricTheCarGuy explains what this check engine code means. This is the less dangerous of the two failures.
- Stuck Closed: This is a serious problem. A thermostat stuck closed traps coolant in the engine and doesn't allow it to reach the radiator. This will cause the engine to overheat quickly, which can lead to severe and expensive damage like a warped cylinder head or blown head gasket. If you see the temperature gauge climbing into the red, pull over immediately and shut off the engine.
Generation Differences: 1st Gen vs. 2nd Gen xB
The Scion xB had two different engines, which use different thermostats and have different replacement procedures.
- 1st Generation (2004-2006): These models have the 1.5L 1NZ-FE engine. The thermostat is relatively easy to access on the lower driver's side of the engine. 🎬 See this 1st Gen thermostat and sensor replacement walkthrough.
- 2nd Generation (2008-2015): These models use the 2.4L 2AZ-FE engine. The thermostat is located in a more difficult spot, and you will likely need to remove the battery and battery tray to get to it. 🎬 Watch: How to replace the thermostat on a 2nd Gen xB.
Choosing the Right Aftermarket Thermostat
While an OEM thermostat from Toyota is always a safe bet, several quality aftermarket options are available. They generally fall into three tiers.
Tier 1: OEM & OEM-Equivalent Brands
These brands are known to manufacture parts for Toyota or produce parts that meet the exact original specifications. They are the most recommended choice for a reliable, stock replacement.
- Aisin: Aisin is a trusted Japanese company that is a direct OEM supplier to Toyota. Choosing an Aisin thermostat is essentially like buying the genuine part without the dealership packaging.
- Beck Arnley: This brand specializes in sourcing parts from OEM suppliers for specific vehicles. A Beck Arnley thermostat for your xB is very likely to be a high-quality, re-packaged OEM part.
Tier 2: Reputable Aftermarket Brands
These brands are well-known in the industry and offer a good balance of quality and value. They are a solid choice for most daily drivers.
- Gates: Gates is a major player in cooling system components, including hoses and belts. Their thermostats are widely used and considered reliable.
- Vemo / Calorstat: These are established European brands that offer quality replacement parts.
Tier 3: Value & Mixed-Review Brands
These brands are often more budget-friendly, but owner experiences can be inconsistent.
- Motorad: This brand has a mixed reputation. While some have used them without issue, others report premature failures. Interestingly, Motorad now owns the Stant brand, which was once highly regarded. They offer a "fail-safe" design that is meant to lock in the open position to prevent overheating.
- Facet: A budget-friendly option that can get the job done, but may not have the same longevity as higher-tier brands.
A Note on "Racing" Thermostats (Mishimoto)
You may see low-temperature or "racing" thermostats from brands like Mishimoto. These are designed to open at a lower temperature (e.g., 155°F instead of 180°F) for highly modified or track-driven cars. For a stock or daily-driven Scion xB, these are not recommended. They can hurt fuel economy, reduce heater performance in winter, and may not provide any cooling benefit in normal driving. Stick to an OEM-temperature thermostat.
Known Issues, Recalls, or TSBs
Searches of the National Highway Traffic Safety Administration (NHTSA) database and technical forums show no specific recalls or widespread Technical Service Bulletins (TSBs) for the engine coolant thermostat on the 2004-2015 Scion xB. Numerous recalls exist for this vehicle, but they are primarily for Takata airbags and do not relate to the cooling system.
| Part/Service | Estimated Cost | Notes |
|---|---|---|
| New Aftermarket Thermostat | $15 - $80 | Price depends on brand and if it includes the gasket. |
| New OEM Toyota Thermostat | $22 - $41 | Does not include labor. |
| Shop Labor | $159 - $233 | Labor costs vary by shop and location. |
| Total Professional Replacement | $200 - $360 | Total cost is typically higher for the 2nd gen xB due to increased labor. |
Pro Tips for Replacement
- Replace the Gasket: Always install a new thermostat gasket. Most new thermostats include one.
- Jiggle Valve Position: The new thermostat will have a small, wobbly pin called a jiggle valve. Install it in the 12 o'clock (top) position to allow trapped air to escape.
- Bleed the System: After refilling the coolant, you must "burp" or bleed the cooling system to remove air pockets. Trapped air can cause overheating even with a new thermostat.
Frequently Asked Questions
What temperature thermostat do I need for my Scion xB?
For a stock vehicle, you should use an OEM-spec thermostat, which is designed to open at 82°C (180°F). Using a lower-temperature "racing" thermostat is not recommended for daily driving.
Should I replace the thermostat housing at the same time?
On higher-mileage vehicles, the plastic thermostat housing can become brittle and crack. While not required, it's a good preventative measure to replace the housing, especially on the 2nd generation xB where access is more difficult.
Can I just remove the thermostat?
No. Running without a thermostat will cause the engine to run too cool, leading to poor performance, bad fuel economy, increased engine wear, and a check engine light. The engine is designed to operate at a specific temperature, which the thermostat helps maintain.
Is it better to buy an OEM or aftermarket thermostat?
Many owners and mechanics recommend using an OEM Toyota part for maximum reliability. However, an OEM-equivalent brand like Aisin will provide the same quality and performance for a lower price.
Helpful Videos
Technical Specifications
OEM Part Numbers: 90916-03093 (For 1.5L 1NZ-FE, 2004-2006) 90916-03136 (For 2.4L 2AZ-FE, 2008-2015) 90916-C3001 (Superseded by 90916-03136)
Standard Opening Temperature: 82°C / 180°F
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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.
- Scion xB:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Is Your Scion xB Thermostat Failing?
- Generation Differences: 1st Gen vs. 2nd Gen xB
- Choosing the Right Aftermarket Thermostat
- Tier 1: OEM & OEM-Equivalent Brands
- Tier 2: Reputable Aftermarket Brands
- Tier 3: Value & Mixed-Review Brands
- A Note on "Racing" Thermostats (Mishimoto)
- Known Issues, Recalls, or TSBs
- Pro Tips for Replacement
- Frequently Asked Questions
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