Engine Coolant Thermostat Guide for the 2007-2012 Mitsubishi Eclipse
Keep your Eclipse engine temperature in check by understanding, diagnosing, and replacing a faulty thermostat.
- A bad thermostat can cause your Eclipse to overheat or run too cold, often triggering the P0128 check engine code.
- For a reliable replacement, choose a quality aftermarket brand like Gates or Beck Arnley, or stick with an OEM part.
- Replacement is a DIY-friendly job for most, but requires draining and refilling coolant.
- Always replace the thermostat gasket and use the correct 180°F (82°C) temperature rating for a stock engine.
Is Your Eclipse Thermostat Failing?
A thermostat is a simple part, but when it fails, it can cause noticeable problems. It can fail in two ways: stuck open or stuck closed. A stuck-closed thermostat is the most dangerous, as it prevents coolant from reaching the radiator, leading to rapid engine overheating. A stuck-open thermostat is more common and will cause the engine to warm up very slowly or not reach full operating temperature at all. This can trigger a check engine light and hurt your fuel mileage.
Common Symptoms of a Bad Thermostat:
- Overheating Engine: The temperature gauge climbs into the red zone, especially in traffic.
- Engine Not Reaching Temperature: The temperature gauge stays low, and the heater may only blow lukewarm air.
- Check Engine Light: A common code associated with a stuck-open thermostat is P0128 (Coolant Temperature Below Thermostat Regulating Temperature). 🎬 Watch: How to diagnose and fix a P0128 fault code.
- Poor Heater Performance: If the engine can't get hot, the cabin heater won't work effectively.
- Temperature Gauge Fluctuations: The needle may swing back and forth erratically.
Choosing the Right Aftermarket Thermostat
When replacing the thermostat on your Eclipse, you have several aftermarket options. The quality can vary, so it's important to choose a reliable brand. OEM is always a safe bet, but quality aftermarket parts can offer similar performance for less money.
Here's a breakdown of the available brands:
- Tier 1 (OEM Quality / Performance): These brands are known for meeting or exceeding original equipment standards. They are a reliable choice for a long-lasting repair.
- Gates: A highly respected name in the aftermarket, often considered OE-equivalent. Gates is a solid choice for reliability.
- Beck Arnley: This brand specializes in sourcing parts that match the original equipment form and function. They often repackage parts from OEM suppliers, so you might find a Motorad or other quality part in the box.
- Mishimoto: Known for performance cooling parts, Mishimoto offers racing thermostats that open at a lower temperature (e.g., 158°F). This can be beneficial for modified or high-performance engines but is not necessary for a stock daily driver.
- Tier 2 (Standard Replacement): These brands offer a good balance of quality and value for everyday use.
- Calorstat / Vernet: A reputable European manufacturer, often an OEM supplier to European car brands. Quality is generally considered good.
- Facet: Another established European brand offering OE-replacement parts.
- Motorad: A very common aftermarket manufacturer. While some mechanics have mixed opinions, they produce thermostats for many other brands, including some in Gates boxes. They are generally a functional and budget-friendly option.
Estimated Replacement Costs
The cost to replace the thermostat can vary based on your engine (2.4L vs. 3.8L) and local labor rates.
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Thermostat | $17 - $72 |
| New OEM Thermostat | $38 - $55 |
| Shop Labor | $100 - $200 |
| Total Professional Replacement | $120 - $275 |
Frequently Asked Questions (FAQ)
Can I replace the thermostat myself?
Yes, for most DIY mechanics, this is a manageable job. 🎬 See this walkthrough on how to change an Eclipse thermostat. It involves draining some coolant, removing the air intake components for access, unbolting the thermostat housing, swapping the part, and then refilling and bleeding the coolant system. The 2.4L engine's thermostat is located on the lower hose side. Ensure the engine is completely cool before starting.
What temperature thermostat should I use?
For a stock 2007-2012 Eclipse, you should use a thermostat with the factory opening temperature, which is typically 180°F (82°C). Using a lower temperature thermostat on a stock engine can prevent it from reaching its optimal operating temperature, potentially affecting performance and fuel economy.
Should I replace anything else with the thermostat?
It is highly recommended to replace the thermostat gasket or O-ring to prevent leaks. It's also a good time to inspect the radiator hoses for cracks or softness and replace them if they are old. Since you'll be draining coolant, it's a perfect opportunity to perform a coolant flush and refill with fresh, manufacturer-specified coolant.
🎬 Watch: How to properly purge air from your cooling system.Are there any recalls for the thermostat on my Eclipse?
No, there are no specific recalls or technical service bulletins (TSBs) from Mitsubishi or the NHTSA for the engine coolant thermostat on the 2007-2012 Mitsubishi Eclipse.
Helpful Videos
Technical Specifications
OEM Part Numbers: MD315301 (for 2.4L Engine) 1305A191 (for 3.8L Engine)
Standard Opening Temperature: 180°F / 82°C
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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.
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