Mazda RX-8 Engine Coolant Temperature Sensor: A Complete Guide (2004-2011)
Understanding this critical sensor is key to the health of your Renesis rotary engine.
- A faulty ECT sensor can cause serious issues, including overheating, which is very dangerous for the RX-8's rotary engine.
- Do not trust the dashboard temperature gauge; use an OBD2 scanner for accurate coolant temperature readings.
- Symptoms include a Check Engine Light (P0117, P0118), poor fuel economy, rough idle, and black smoke.
- For this critical part, choose high-quality aftermarket brands like NGK/NTK or Delphi, or stick with the Mazda OEM part.
Symptoms of a Failing RX-8 Coolant Temp Sensor
A bad engine coolant temperature sensor can cause a variety of problems, some of which can be mistaken for other issues. Because the sensor's reading affects so many engine functions, failure can lead to poor performance and potentially serious issues if ignored.
- Check Engine Light: This is the most common sign. The system will often trigger codes like P0117 (Circuit Low) or P0118 (Circuit High).
- Poor Fuel Economy: If the sensor incorrectly tells the ECU the engine is cold, the computer will enrich the fuel mixture, causing the car to use more gas than necessary.
- Rough Idling and Stalling: An incorrect temperature reading can lead to the wrong fuel and air mixture, causing the engine to idle poorly or even stall, especially when cold.
- Black Smoke from Exhaust: A rich fuel mixture from a bad sensor reading can result in unburned fuel exiting through the exhaust, creating black smoke.
- Engine Overheating: If the sensor fails to report that the engine is hot, the cooling fans may not turn on when needed, leading to overheating. This is especially dangerous for a rotary engine.
- Hard Starting: The ECU relies on the ECT sensor for cold-start adjustments. A bad signal can make the car difficult to start.
A Note on the RX-8 Dashboard Gauge
Many RX-8 owners know the factory temperature gauge on the dashboard is not very precise. It is often called a "dummy gauge" because it tends to stay in the middle position across a wide range of temperatures and may only show "hot" when the engine is already dangerously overheated. Do not rely on it to diagnose cooling system problems. An OBD2 scanner that shows live data provides a much more accurate reading from the ECT sensor.
Choosing a New Aftermarket ECT Sensor
For the Mazda RX-8, the OEM sensor (part number B593-18-840A) is a reliable choice. However, high-quality aftermarket sensors can offer identical performance for a lower price. Given the critical nature of this part for the rotary engine, it's best to stick with reputable brands.
Here’s a breakdown of common aftermarket brand tiers:
- Tier 1 (OEM Quality): Brands like NGK/NTK and Delphi are often original equipment suppliers to many car manufacturers. They have a strong reputation for quality and reliability, making them a safe bet for your RX-8.
- Tier 2 (Reputable Aftermarket): Brands like Beck Arnley, Standard Ignition (SMP), and Holstein are well-known in the aftermarket world. They generally provide good quality parts that meet or exceed OEM specifications and are a solid choice.
- Tier 3 (Value-Oriented): Brands like Global Parts and others may offer the lowest price, but their quality can be inconsistent. For a part this critical to the RX-8's engine health, it's often worth spending a few extra dollars for a more reputable brand.
Pro Tip: Coolant Level vs. Coolant Temperature
The RX-8 has two different sensors. The Engine Coolant Temperature Sensor (the subject of this article) reads the temperature. There is also a Coolant Level Sensor in the overflow tank that is notorious for failing and causing the coolant light to come on even when the level is fine. If your coolant light is on but the car isn't overheating, you may be dealing with the level sensor, which requires replacing the entire overflow bottle.
Cost to Replace an RX-8 Coolant Temperature Sensor
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Sensor | $13 - $41 |
| New OEM Sensor | $50 - $65 |
| Shop Labor | $85 - $130 |
| Total (DIY) | $13 - $41 |
| Total (Installed at Shop) | $98 - $171 |
Note: Costs are estimates and can vary based on location and specific repair shop rates. The labor estimate is for replacing the sensor only.
Frequently Asked Questions
Where is the coolant temperature sensor located on a Mazda RX-8?
The engine coolant temperature sensor on the 2004-2011 Mazda RX-8 is located on the engine block, near the thermostat housing. It is somewhat hidden under the alternator on the passenger side of the engine bay.
Can I drive my RX-8 with a bad coolant temp sensor?
It is not recommended. A bad sensor can cause the engine to run too rich, leading to poor fuel economy and potential carbon buildup. More critically, it could fail to trigger the cooling fans, leading to a catastrophic overheating event, which is especially damaging to a rotary engine.
Are there any recalls for the RX-8 coolant temperature sensor?
No specific recalls have been issued by the NHTSA for the engine coolant temperature sensor on the 2004-2011 Mazda RX-8. Searches for Technical Service Bulletins (TSBs) also did not reveal any specific issues directly related to this part for this vehicle, though other Mazda models have had TSBs for different coolant sensors.
Is replacing the RX-8 ECT sensor a good DIY job?
Yes, for someone with basic mechanical skills. The main challenges are accessing the sensor, which is a bit tucked away, and the need to drain some coolant to avoid a mess. The sensor itself simply unscrews. Always make sure the engine is completely cool before opening the cooling system.
Technical Specifications
OEM Part Numbers: B593-18-840A B593-18-840
The sensor is a 2-pin thermistor that threads into the engine block near the thermostat housing.
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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.
- Mazda RX-8: