Subaru RX Coolant Temperature Sensor Guide (1986-1989)
Solving engine issues in your RX starts with understanding this critical sensor.
- A failing sensor will most likely cause poor fuel economy, black exhaust smoke, and a rough idle.
- Ensure you are replacing the two-wire ECU sensor, not the single-wire gauge sender.
- For this vehicle, a new aftermarket part is the most practical and available option.
- The sensor is located under the intake manifold and can be difficult to access.
Is Your Subaru RX Running Rough? Check the Coolant Temp Sensor
If your 1986-1989 Subaru RX is experiencing poor fuel mileage, a rough idle, or has trouble starting, a failing coolant temperature sensor could be the culprit. This sensor tells the engine's computer how hot or cold the engine is, which affects how much fuel is injected. A bad sensor can trick the computer into thinking the engine is always cold, leading to a rich fuel mixture that causes performance issues.
Symptoms of a Failing Coolant Temperature Sensor
Because this sensor is critical for fuel management, a failure will usually cause noticeable problems. Here’s what to watch for:
- Poor Fuel Economy: One of the most common signs. A faulty sensor sending a constant "cold" signal makes the ECU inject more fuel than needed, hurting your gas mileage.
- Black Smoke from Exhaust: This is a direct result of too much fuel being injected. The unburned fuel exits through the exhaust, creating black smoke.
- Difficulty Starting: When the ECU gets an incorrect temperature reading, it can't provide the right fuel mixture for starting, whether the engine is hot or cold.
- Rough Idle and Stalling: An improper air-fuel ratio can make your engine run rough, shake at idle, or stall completely.
- Check Engine Light: Even on pre-OBDII vehicles like the RX, a sensor failure can trigger the check engine light.
- Cooling Fan Issues: The sensor also helps control the electric cooling fans. A bad sensor might prevent the fans from turning on, leading to overheating.
Don't Confuse the Sensors
Your Subaru RX has two different sensors. The one that controls the engine is the two-wire Coolant Temperature Sensor (for the ECU). There is also a single-wire temperature sender that only operates the dashboard gauge. Replacing the wrong one won't solve your engine performance problems.
Choosing the Right Aftermarket Part
For a classic vehicle like the 1986-1989 Subaru RX, finding new original equipment (OEM) parts is often impossible as they have been discontinued. This makes high-quality aftermarket parts the go-to solution for keeping these cars on the road. The available 'Replacement' brand sensor is designed to be a direct-fit, affordable, and reliable alternative that meets original factory specifications. It provides the same function as the original part, ensuring your RX's ECU gets the accurate temperature readings it needs to run efficiently.
| Part Type | Estimated Cost |
|---|---|
| New OEM | $75 - $120+ (if found) |
| New Aftermarket (Replacement) | $17.82 |
| Used OEM | $10 - $30 |
| Shop Labor for Installation | $90 - $150 |
Pro Tip: Check the Connector First
On older vehicles, the plastic electrical connector and wiring can become brittle and corroded. Before replacing the sensor, inspect the connector and wires for damage or corrosion. Sometimes, simply cleaning the contacts with electronic cleaner can solve the problem.
Frequently Asked Questions (FAQ)
Where is the coolant temperature sensor located on my Subaru RX?
The ECU coolant temperature sensor on the EA82 turbocharged engine is located on the coolant crossover pipe, which sits under the intake manifold, often near the turbo. It can be difficult to see and may require removing the air intake plenum to access it. It is the sensor with a two-wire electrical connector.
Is it hard to replace this sensor myself?
The replacement itself is simple—you just unscrew the old sensor and screw in the new one. However, the location is tight and hard to reach, which increases the difficulty. It may require removing other parts to get to it. For a patient DIY mechanic with the right tools, it is feasible. The job typically takes about an hour.
Are there any recalls or TSBs for this part?
Searches of the National Highway Traffic Safety Administration (NHTSA) database and other technical resources show no specific recalls or technical service bulletins (TSBs) for the coolant temperature sensor on the 1986-1989 Subaru RX.
What happens if I ignore a bad coolant temperature sensor?
Ignoring a bad sensor can lead to more serious problems. Persistently running a rich fuel mixture can foul spark plugs and damage the catalytic converter. More critically, if the sensor fails to signal an overheating condition, it could lead to severe engine damage from overheating.
Technical Specifications
Connector Type: 2-wire plug
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.
- Subaru RX: