Your Guide to the 1977-1978 BMW 630CSi Coolant Temperature Sensor
Understanding the critical sensor that feeds temperature data to your classic 6-Series' fuel injection computer.
- This sensor is critical for the L-Jetronic fuel injection, not the dashboard gauge.
- Symptoms of failure usually relate to a rich fuel mixture, like bad gas mileage and a rough idle.
- Replacement is simple and can be done with basic tools when the engine is cold.
- No recalls or TSBs are known for this specific part on your vehicle.
Understanding Your M30 Engine's Fueling Brain
Your 1977-1978 BMW 630CSi uses a Bosch L-Jetronic fuel injection system, which was quite advanced for its time. This system depends on several sensors to keep the M30 engine running efficiently. The coolant temperature sensor (CTS) is one of the most important, telling the engine's computer (ECU) how hot or cold the engine is. A wrong signal can cause many running problems, making a good sensor essential for performance and reliability.
Symptoms of a Failing Coolant Temperature Sensor
When the CTS fails, it usually sends a false "cold" signal to the ECU. This tricks the computer into injecting too much fuel, as if the engine is always cold. Here’s what to look for:
- Poor Gas Mileage: The most common symptom is the engine running rich and wasting fuel.
- Black Smoke from Exhaust: A very rich fuel mixture can result in unburned fuel exiting through the exhaust as black smoke.
- Rough Idle and Misfires: An incorrect fuel-to-air ratio can cause the engine to idle poorly or misfire.
- Hard Starting: If the sensor incorrectly tells the ECU the engine is warm when it's cold, it won't provide the extra fuel needed for a cold start.
- Failed Emissions Test: High levels of unburned hydrocarbons from a rich mixture will cause the vehicle to fail an emissions test.
Choosing the Right Aftermarket Sensor
For a classic BMW, part selection is important. The original sensor was made by Bosch, and the ECU is designed for its specific electrical resistance values. Using a sensor that doesn't match these values can cause subtle running issues that are hard to diagnose.
The "Replacement" brand sensor is a budget-friendly choice. For a critical part like the ECU temperature sensor, it's important to weigh the cost savings against the potential for performance issues. While it may function, its electrical characteristics might not perfectly match the original Bosch specifications that your L-Jetronic system expects. For a sensitive system like this, investing in a higher-quality part from a known OE-supplier like Bosch is often the safer choice to ensure proper engine function.
| Part Tier | Brand(s) | Cost Estimate | Notes |
|---|---|---|---|
| New OEM-Equivalent | Bosch | $17 - $25 | As the original supplier, this is the safest choice for correct performance. |
| New Aftermarket | Replacement, FAE, Standard | $12 - $18 | A cost-effective option. Ensure the part is a direct cross-reference for your vehicle. |
| Shop Labor | N/A | $50 - $100 | This is a quick job, typically taking less than an hour. |
Frequently Asked Questions (FAQ)
Where is the coolant temperature sensor located on a 1977-1978 BMW 630CSi?
The sensor is located in the thermostat housing at the front of the M30 engine. You will typically see two or three sensors clustered together. The one for the ECU usually has a two-pin connector.
Is this a difficult part to replace myself?
No, this is a good DIY job for a beginner. It requires basic tools to unplug the electrical connector and unscrew the sensor. Be prepared for a small amount of coolant to spill. It is best to perform the replacement when the engine is cold.
Are there any recalls for this part?
No, searches of the National Highway Traffic Safety Administration (NHTSA) database show no recalls or Technical Service Bulletins (TSBs) specifically for the coolant temperature sensor on the 1977-1978 BMW 630CSi.
What happens if I ignore a bad sensor?
Ignoring a bad sensor will lead to poor fuel economy, rough running, and potentially damage to your catalytic converter over time due to the excessively rich fuel mixture. It can also make the car difficult to start.
Technical Specifications
OEM Part Numbers: 13621357414
Connector: 2-Pin. Type: Negative Temperature Coefficient (NTC). Resistance at 20°C (68°F): Approximately 2.1k - 2.9k Ohms.
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.