Thanks for the fast replies and advice.
I am worried that my temp gauge is not showing an accurate temp reading, thus the panic when it went up so high after replacing the old thermostat. I should probably get the car temp tested and go from there. Do you think I should put the new thermostat back in? I always thought a bad thermostat will cause overheating. Live and learn, he?

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1982 Mercedes-Benz 300SD 210k miles