Coolant flush

[Eisaia]

2008 Silverado 1500 5.3l Gas

 

How can I tell if the new thermostat is opening correctly 

[Black02Silverado]

I always check mine before I put it in.  I put it in a pot of water and watch it as the water starts to boil. 

 

As for installed, keep an eye on your temp gauge and it should be the same as before you replaced the thermostat.

[dna9656]

The upper radiator hose will get hot when it opens so if you can monitor both the temperature of the hose and the temp gauge you'll get a good idea of what's going on. You could also tape a thermometer to the upper hose and watch it as the engine warms up. If your temp gauge isn't working it could be the temp sensor or the wiring that connect the sensor and the gauge together.