Can't figure out the problem! 1990

[zcoop]

My century overheated and so I have been working on it to get some repairs done and so far this is what I have replaced:
Radiator
Radiator cap
Thermostat
Thermostat gasket
Thermostat housing gasket

My temperature has been fluctuating still though, it will go up to somewhere between 200-220 and then drop.
I have tried burping it and when I drive it I am not losing coolant. I also tried a block test thinking that there might be something wrong with the head, but the test came out negative. Is there any more advice that anyone has on what I may need to do to fix the problem with my temperature going up and dropping?

 

[ryenie]

I think i would try flushing the cooling system next. How quickly does it reach above 200, and how far does it drop when it drops?

 

[CorvairGeek]

What happened when it originally overheated?
Is the engine cooling fan operating when it gets to around 220 degrees and the temperature drops?
The cooling fan doesn't turn on until around 215 degrees. It operates (nearly) constantly when the A/C or defroster is on (if the refrigeration system is operational), so the car will appears to run cooler and a more even temperature.
I will add that unless you bought an OEM or a higher priced aftermarket / premium / high accuracy thermostat, they are absolutely terrible and will cycle temperature all over the place (the one on the 3300 is so hard to reach I would never chance a cheap one).

 

[Lubener]

With all you have done, did you check the accuracy of the temp gauge itself? Sending units often get flaky after an overheating event.

 

[ServantToTruth]

With all you have done, did you check the accuracy of the temp gauge itself? Sending units often get flaky after an overheating event.

How should that be done ?

 

[ryenie]

How should that be done ?

With an infrared thermometer.