ive got an 05 civic ex se coupe 1.7 mt vtec that ive had for 1.5 yrs. love it, no problems till now. it started leaking coolant a couple times, not continuously, after i drive it kinda hard. and determined it was coming out of the resivour, which was overfilled almost to the cap. mind you, i havent put any coolant into the thing. i took off the radiator cap to see if the seal was bad, and it let out a huge gasp of air and the level in the res went down to normal after i ran it once, so im assuming air pocket. the next day it started overheating and the coolant level went back up. the next day (yesterday) i tried getting it to overheat again to see if its consistant, nothing happened. i changed the thermostat cause its quick easy and cheap, then i tested the old one and it still worked.

anyone have any ideas? im lost

 

When does it overheat? Is it only during city driving? Is the radiator fan kicking in?

 

it only overheated once and it was after a stoplight. fans still work. im hoping it was just an air pocket that got cycled out when i changed the thermostat because it hasnt overheated again..

 

I had the same problem, ended up being a slow head gasket leak. Had it changed and all the problems went away.