Nissan Repair: headgaskets, nissan sentra, air bubbles

Question
i recently changed my antifreeze on my 2002 nissan sentra 2.5l 4cyl.

about 3 days later i notice my check engine light came on. it showed as a misfirein cylinder 3.

after a compression test i had air bubbles in the radiator.

my question is?
if i had an air pocket in the cooling system would i have noticed any overheating prior to the damge?
do you think changing the antifreeze caused the headgasket to go?

thanks
jim

Answer
Jim,

Changing the antifreeze did not cause the leak.  But, it probably helped it come on since the old coolant was cleaned out and that small leak opened up with the fresh water and antifreeze.  I would not attribute the problem to the change but it helped the problem show up.  An air pocket would hot have manifested itself in the head so that would not have caused the leak so I bet the problem just opened itself up with the change since the gunk and such was flushed out with the change.