cool down vs cool off

cool down

verb
  • To decrease in degree or intensity. 

  • To become cooler; to be reduced in temperature. 

  • To become less agitated or excited. 

  • To cause (something) to become cooler; to reduce the temperature of. 

  • To cause (someone) to become less agitated or excited. 

cool off

verb
  • To decrease in temperature, activity, or temper. 

  • To cause to decrease in temperature, activity or temper. 

How often have the words cool down and cool off occurred in a corpus of books? (source: Google Ngram Viewer )