1998 Chevy Cavalier no leak found

I replaced the water pump, head gasket, new thermostat. Still overheating and no leak anywhere but it spitting back out the water bottle. Noticed that the thermstat is not opening even at 230 degree. Nothing wrong with the radiator. Left the thermostat out and temp ran below normal. Is the Stant company not quaity checking their product anymore that we need to check it on the stove burner using hot water and candy therm to see if it open at 180 degree? Feel like it is made oversea now that product is poor. I found two therm rated at 195' and open at 220'. Brand new!