1987-1989 Chevrolet P20 Coolant Temperature Sensor Guide
Fix poor fuel economy and rough running in your P20 by understanding this critical engine sensor.
- Verify you are replacing the two-wire ECT sensor for the computer, not the one-wire sender for the dashboard gauge.
- A bad ECT sensor is a common cause of poor fuel economy, black exhaust smoke, and a rough idle.
- Replacement is simple, requires basic tools, and can be done in under 30 minutes with a cool engine.
- For this vehicle, a quality aftermarket sensor is a reliable and cost-effective repair solution.
Is It the Coolant Sensor or the Temp Sender?
Your Chevrolet P20 has two similar-looking sensors for temperature. It is critical to identify the correct one before buying a replacement. The most common ordering mistake is buying the wrong part.
- Engine Coolant Temperature (ECT) Sensor: This sensor communicates with the engine's computer. It has a two-wire electrical connector and directly affects engine performance, fuel economy, and emissions. This is the part that fixes the symptoms described in this guide.
- Temperature Sender/Switch: This part communicates with the temperature gauge on your dashboard. It typically has a single-wire connector. If your gauge is not working but the engine runs fine, the sender is likely the problem, not the ECT sensor.
Symptoms of a Failing Coolant Temperature Sensor
When the ECT sensor fails, it often sends a false signal to the computer, making it think the engine is permanently cold. This can cause a number of noticeable problems:
- Poor Fuel Economy: The computer provides too much fuel, thinking the engine is still warming up. This is one of the most common symptoms.
- Black Smoke from Exhaust: The excessively rich fuel mixture doesn't burn completely in the cylinders and instead burns in the hot exhaust pipe, creating black smoke.
- Check Engine Light: The engine computer will detect a signal from the sensor that is out of the expected range and trigger a warning light. On these models, this may result in OBD-I codes 14 or 15.
- Rough Idle and Stalling: The incorrect air-fuel mixture can make the engine run poorly, especially at idle or during cold starts.
- Engine Overheating: In some cases, a faulty sensor can prevent the electric cooling fans (if equipped) from turning on when they should, leading to overheating.
Choosing the Right Aftermarket Part
For a workhorse vehicle like the 1987-1989 P20, finding original OEM parts can be difficult and often unnecessary for simple components like sensors. The aftermarket provides reliable and affordable solutions.
The available Replacement brand sensor is a cost-effective choice that meets the original specifications for fit and function. For an older, straightforward engine management system like the one in the P20, a standard aftermarket sensor is a perfectly suitable repair that will restore proper engine function without the high cost or scarcity of an OEM part.
| Part or Service | Estimated Cost |
|---|---|
| New Aftermarket Coolant Temp. Sensor | $18.79 |
| Shop Labor | $90 - $150 |
| Total Estimated Cost (Professional) | $108 - $168 |
Frequently Asked Questions (FAQ)
Can I replace the coolant temperature sensor myself?
Yes, this is a very DIY-friendly job, even for beginners. It requires basic hand tools, primarily a deep socket and ratchet. The sensor is usually easy to access on top of the engine near the thermostat housing.
Where is the ECT sensor located on the P20?
On Chevrolet engines from this era (like the 5.7L V8), the ECT sensor is typically screwed into the intake manifold or cylinder head, near the thermostat housing at the front of the engine. Look for a brass sensor with a two-wire connector.
Do I need to drain all the coolant to replace it?
No, you do not need to drain the entire cooling system. A small amount of coolant will leak out when you remove the old sensor. The key is to have the new sensor ready to install immediately after removing the old one to minimize coolant loss. Always perform this job on a completely cool engine to avoid burns.
What happens if I don't replace a bad sensor?
While you can often still drive the vehicle, you will continue to have poor performance and terrible fuel economy. Over time, running constantly rich can damage other components like the oxygen sensor and catalytic converter, leading to more expensive repairs.
Technical Specifications
Connector: 2-wire plug. Location: Typically near the thermostat housing on the intake manifold.
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.
- Chevrolet P20: