Ok, this may be a dumb question but I can't find a simple answer. I changed out my water pump with a bad bearing. I also changed the alternator, unfortunately it's the wrong alternator, i'll get to that tomorrow when the right one comes in. I cranked the car and immediately the "TEMP" light came on. What does this mean? also, I shut it down after about a minute and i guess the coolant worked it's way in the system and i had to add almost another 1/2 jug of coolant. Have not been able to test again to see if that was why the light went on or not. Just not sure what the temp light means... does it come on at "X" temp and where is it connected to the engine? is it possible it got compromised in the changing of the water pump?

Sorry if this is a dumb question.

 

Because of air bubbles you did not have enough coolant in the system when you first started the engine, this allowed the engine to overheat. When the bubbles came out the coolant level dropped and you had to add more coolant. You may have to repeat procedure several time until all the air works its way out of the system.

 

I don't think you technically overheated the engine, since the light went on right away. But your coolant level in the block was low, and the heads likely got a bit toasty, which is also where the sending unit is located. Don't know that I would trust what the sending unit was "reading" anyway, as it's designed to read coolant temperature, not air pocket temperature.

 

I have a temp gauge as well... i'm not sure where it reads the temp from the engine, it definitely works as you can see the temp rise and when i park it goes up a bit... not sure on accuracy.

 

As said, a sensor reads liquid better than air.
The TEMP light will come on in START position as a bulb test.
You can mentally calibrate the gauge with the present thermostat.
Feel the upper hose and when it gets hot, t/stat opened at its stamped opening temp, check gauge indication.
Now you know the two are mentally calibrated.