I was wondering if your temp gauge needles actually move constantly or does it hit a certain spot and stays there? Mine always sits 3/4 of the way up and never moves no matter how hot or cold the weather gets. As soon as the car's warmed up in the winter, it stays there until I shut the car off. Where does the gauge get its reading?

 

mine stays at the middle all the time. it went up when my radiator screwed up. but now its back to normal at the middle.

-phil

 

The temp gauges in most cars are built with a large area of hysteresis in the middle. That is, they are accurate only at the extremes, and in the middle, the same reading can vary 30-40 degrees. This is done to keep the average Joe Car-Owner from getting freaked out when his temp gauge moves all the time. You'd probably see a 30-40 degree swing in normal operation.

There are three or four temp senders in the engine (IIRC, autos have an additional one in the radiator). IIRC, the temp gauge reads off the end of the underside of the thermostat housing, the fan switch reads off the outside of the thermostat housing, and the engine controller (ECU) reads off the sensor in the back of the cylinder head.