temp sending unit 3.4

i have a 95 lumina ls 3.4 124k i replaced the thermostat that someone didnt have in the car now that i put one in it the car keeps readin that its getting hot after driving for 2-3 mins could it be a bad temp sending unit an if so weres it located at on the 3.4

Check for air in the system first, did you bleed it after refilling?

ya i thinkin i bleed it right not for sure if i did it right i got a good flow outa the front one but cant seem to get a steadt stream out the back one.. this is my first chevy.. just in case i didnt do it wright whats the proper way to bleed it out..

Get it hot enough to open the t'stat, bleed one at a time till a steady stream of coolant comes out.