Coolant Temp Sensor for BMW 318i 320i 325i M3 520i 525i M5 730i 735i E28-E36

The most common test is to measure the sensor resistance with a multimeter at a known coolant temperature and compare against the manufacturer resistance curve. A cold engine (20 degrees C) typically reads 2,000 to 3,000 ohms and drops to around 200 to 300 ohms at operating temperature (90 degrees C). An OBD2 scanner showing a fixed temperature reading that does not change as the engine warms up is also a strong indicator of sensor failure.

Indirectly yes. If the sensor reports a lower temperature than actual, the ECU may not activate the cooling fan at the correct time, allowing the engine to overheat. It can also suppress the dashboard warning light, meaning you may not be alerted until the engine is already at a dangerously high temperature. Replace a suspected faulty sensor promptly.

Not always - many coolant temperature sensors can be replaced quickly with minimal coolant loss if you work fast and have a replacement ready to thread in immediately. However on some vehicles the sensor location requires partial coolant drainage. Check the sensor position on your specific engine before starting. Always use fresh coolant when topping up after replacement.

Symptoms include poor fuel economy, black smoke, engine overheating warning, incorrect temperature gauge reading, hard starting when cold, and rough idle. Fault codes P0115 to P0119 are commonly associated with coolant temperature sensor faults.

A faulty coolant temperature sensor can cause the ECU to run rich fuel mixtures and prevent the cooling fan from operating correctly, risking engine overheating. Replace it promptly - it is a low-cost part that can prevent expensive engine damage.

A faulty thermostat typically causes the engine to overheat or never reach operating temperature. A faulty coolant temp sensor causes incorrect gauge readings and running issues but the coolant itself may be at the correct temperature. An OBD2 scanner showing live coolant temp data helps distinguish between the two.

Many vehicles have two sensors - one for the ECU (engine management) and one for the dashboard temperature gauge. They look similar but are not interchangeable. Check your vehicle's service manual or contact us with your vehicle details to confirm which sensor you need.