Water temp sensor function
 

1989 740 GL . Just curious on the functioning range of the WT sensor. In the cold weather the car starts and idles around 1200 rpm and then settles down to 650 +/-. Now that the warm weather is here at 75* and a cold start it just goes to normal 650 idle. Assuming the sensor is a variable resistor at what temperature would it transition from high idle to low idle. My green book doesn't provide me with any values .

Even in warm temperatures, I would expect the engine to fast idle for a moment and then settle down. If I recall, on the old red block, there is an engine temperature sensor down under the intake manifold and difficult to get to.

indeed, in fact there are two temp sensors, one is used for the dashboard gauge and has just a single pin, the other is used by the ECU and ICU and has 2 pins. both of these are screwed into the side of the engine under the intake manifold... depending on the specific version car and year, hte position has bounced around some between the two sensors.

Would you happen to know what the values of each of the 2 pins are. I know where the rear water temp. sensor is so I'd like to take a reading . Thanks.

either pin to ground (body), for an LH 2.4 car (1989+), nominal values are...

32F (0C)-- about 6000 ohms within a range of +/- 10%
68F(20C) -- about 2300 ohms
104F(40C) -- about 1300 ohms
140F(60C) -- about 600 ohms
176F(80C) -- about 300 ohms
212F(100C) -- about 190 ohms


the two pins are two seperate sensors, one is wired to the ECU (fuel injection control unit), and the other to the ICU (Ignition control unit)

Thank You