For a complete cooling system drain, there are 3 points.

1. Open petkawk at bottom passenger side of the radiator.
AND
2. Open thrmostat housing.
AND
3. Remove drain plug on bottom of the water pump.

Your distilled water flush would be best accomplished with no thermostat installed.

GM says "drinkable" water. Depends on which type and concentration of chlorine is in your water. Generally, chlorine and aluminium don't get along well.

Spellcheck flagged the Canadian spelling.

I flush already the radiator with destille water, now is keep cool, do I have to disconnect the battery before replacing the thermostat? or is not necessary?

Always a good idea when there’s wires in the way. But not really necessary

I change the thermostat for the AC Delco 131-158 and flush the radiator yesterday I finish,I put new coolant DEX-COOL, today was ok at the morning was ok on the highway, but afternoon when I finish my job and back to my home on the highway happens de same, the thermostat go down and show - - 0 grade celsius, with any code , just reset the code with Torque software and back to alive with current temperature 77 or 78, depending, so my question is if I change the DEX-COOL and change the thermostat, could be the cooling sensor temperature?, any suggestion pls. thanks

Did you burp the air out of the cooling system?

https://www.chevyhhr.net/forums/how-...-system-60614/

Thanks oldblue, yes I did yesterday afternoon and today morning, keep the car in my driveway with the front more high all night and and the morning I put more dex-cool and tun on the heating for about 5 minutes, and was ok because the temperature from myhome to my work was ok under 80 , keep in 79, 78, so I leave the car in the street park in my work and when I finish my job I drove back to my home, but for about 40 minutes after drive, I saw the temperature show 0(dash dash - -), when I reset start up until 93, I park in parking lot for pizza pizza and put more dex-cool and when back to my home I leave in my driveway and I did the same put more with heating on(for about 5 minutes), so just I burp two time only, and the procedure have to be more.., so tomorrow I will see what happens...

Sometimes you need to burp it 5 or 6 times

yes I did couple time and now is working properly, thanks oldblue

Could be the ECT (temp sensor).