I agree, like I said earlier, the original sensor was red, where as this one is green. Could it have different voltage readings, and isn't moving the gauge much. I did notice when I started the engine and gave it gas, the needle moved a little to the top of the 4 in 40C on the gauge. No matter how long the car runs it won't go higher. I find it hard to believe the car runs at 40C( approx 107 F). As I stated I just rebuilt the engine and don't want to drive it with bad temp reading. And yes the sensor is in a passage with coolant in it.