96 blazer new radiator still over heats

replaced the thremostat and the radiator, ran fine for about a 40 mile trip then ran it a second trip, started to run hot about 220, then would go down to 200 back and forth for about a 10 mile run. I didnt swith the radiator cap, that may be an issue?? Not really to sure?

replaced the thremostat and the radiator, ran fine for about a 40 mile trip then ran it a second trip, started to run hot about 220, then would go down to 200 back and forth for about a 10 mile run. I didnt swith the radiator cap, that may be an issue?? Not really to sure?

Is the tempt gauge working good?
Is the stat good?
Rad full of coolant?
Any coolant boil over in catch tank?

Is the tempt gauge working good?
Is the stat good?
Rad full of coolant?
Any coolant boil over in catch tank?

Everything was full when I drove yesterday, The radiator was switched and all new fluids. Checked everything... but this morning the coolant was empty in the resevoir.

Everything was full when I drove yesterday, The radiator was switched and all new fluids. Checked everything... but this morning the coolant was empty in the resevoir.

Is the engine tempt gauge working right.
Check engine running tempt gauge with a thermoter or with the PCM temp senser reading.

Did you burp it when you installed stat and rad?

Is the rad still full?

Fill rad and coolant tank and see what it does.

Is thermo stat good?