A Deep Dive into the Engine Coolant Thermostat for the 2006-2016 Mazda MX-5
Understanding the most common cooling system failure on the NC Miata and how to choose the right replacement part.
- The most common failure for the NC MX-5 thermostat is sticking open, which causes the engine to run too cool.
- Symptoms include a slow warm-up, a temperature gauge that drops at highway speeds, and a P0128 check engine light code.
- Replacement thermostats come as an integrated unit with the housing; standard replacements like Gates are best for street use.
- The job is DIY-friendly but requires removing the throttle body and carefully bleeding the cooling system.
Is Your MX-5's Thermostat Failing?
Thermostat failure is a very common issue on the 2006-2016 (NC) Mazda MX-5. Unlike many other cars where a stuck-closed thermostat leads to overheating, the most frequent failure on the NC Miata is the thermostat getting stuck in the open position. This creates a different set of problems that can be confusing if you're expecting to see a temperature gauge in the red.
Symptoms of a Failing Thermostat
- Engine Takes Forever to Warm Up: This is the most common sign. The engine struggles to reach its normal operating temperature.
- Temperature Gauge Drops at Speed: When cruising on the highway, the increased airflow over the radiator cools the engine too much, causing the temperature gauge to fall from the middle towards the 1/4 mark.
- Poor Heater Performance: Because the engine isn't getting hot enough, the heater in your cabin will only blow lukewarm air.
- Check Engine Light: The car's computer expects the engine to warm up within a certain time. When it doesn't, it can trigger a Check Engine Light with the code P0128 (Coolant Temperature Below Thermostat Regulating Temperature).
A Note on Overheating
While less common, a thermostat can fail in the closed position. This is a much more serious problem. It will trap coolant in the engine and cause it to overheat very quickly. If you see your temperature gauge climbing into the red, pull over and shut off the engine immediately to prevent severe damage.
Choosing the Right Aftermarket Thermostat
When shopping for a new thermostat for your MX-5, you'll find it comes as a complete unit with the housing. You have a choice between standard replacement parts and performance-oriented options.
Brand Tiers: Standard vs. Performance
- Standard Replacement (Gates): Brands like Gates are considered OEM-equivalent, meaning they are designed to work just like the original part from Mazda. They are a reliable and cost-effective choice for daily driving and spirited street use. They will have the stock opening temperature of around 182°F (82°C).
- Performance (Mishimoto): Mishimoto offers a "racing" thermostat that opens at a much lower temperature, around 155°F. The goal is to start the cooling process sooner, which can be beneficial for track cars that operate under extreme heat. However, for a street-driven car, this can be a problem. The engine may run too cool, leading to reduced fuel efficiency, potential check engine lights, and poor heater performance. This is best left for dedicated track builds.
Long Neck vs. Short Neck
There are two designs for the thermostat housing outlet: a "long neck" and a "short neck". Most aftermarket parts are the long neck version. This part will fit all 2006-2016 models, but if your car originally had the short neck version, you may need to trim about an inch off your upper radiator hose 🎬 See a full maintenance walkthrough for the thermostat and coolant. for a perfect fit.
| Part Type | Estimated Cost |
|---|---|
| New OEM (Mazda) | $80 - $110 |
| New Aftermarket (Gates, Mishimoto) | $40 - $92 |
| Shop Labor | $150 - $250 |
Frequently Asked Questions (FAQ)
Is replacing the thermostat a DIY job?
Yes, it is a manageable DIY job for someone with basic mechanical skills. The thermostat is located under the throttle body, so you will need to remove the airbox and throttle body to get to it. The bolts can be tricky to reach, and bleeding the air from the cooling system afterward is a critical step that must be done correctly. 🎬 Watch: How to properly bleed air from the cooling system. Expect it to take 1-2 hours.
🎬 Watch this step-by-step guide to replacing your NC thermostat.Are there any recalls for the thermostat?
No, there are no official recalls or widespread Technical Service Bulletins (TSBs) from Mazda or the NHTSA for the engine coolant thermostat on the 2006-2016 MX-5.
Should I use a lower temperature "racing" thermostat?
For a daily driven or street car, no. A lower temperature thermostat like the one from Mishimoto is designed for race cars. On the street, it will likely cause your engine to run too cool, which can hurt fuel economy and may even trigger a check engine light. Stick with a standard, OEM-temperature thermostat for the best all-around performance.
What coolant should I use when I refill the system?
Mazda specifies FL22 long-life coolant. It is important to use this type or a compatible Asian vehicle coolant. Do not mix it with other types of coolant. When refilling, you will need a 50/50 mix of coolant and distilled water.
Helpful Videos
Technical Specifications
OEM Part Numbers: LF70-15-170 LFE2-15-170
Standard Opening Temperature: 82°C (180°F). Comes as an integrated unit with housing.
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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