I have a 2000 si and it ran hot at idle a few days ago. it was only maybe for 30 seconds at the most but i herd the radiator cap hissing and then the smoke from under the hood, looked at the needle and it was pegged. I pulled over immediately and shut the car off and let it cool. I was able to get only about half a liter of water in it and drove it home and drove it to work the next day and it seemed to run fine. Took it out the following night for some spirited back roads driving and first gear seemed to pull fine at wide open throttle but at around 6500 t0 7000 i notice the car had a loss of power. Almost like vtec shut of. Like a loss of maybe 30 hp or so but vtec was still singing in my ears, i could hear the difference like say if oil pressure dropped and vtec disengaged while at wide open throttle , This was not the problem, it was just loosing power in that rpm range. Second gear was the same and so was 3rd and i never went higher in wide open throttle with it acting like this. Second and third were more obvious cuz of the taller gearing and the car taking longer to get from 6500 to red line so it was an obvious longer wait for red line than usual. Anybody have any ideas? Blown head gasket? something else?Im a great do it yourself mechanic and have worked on this car for 9 years and 97000 miles so any topic i can follow. THANKS SO MUCH!!!

 

like always when overheating you should check the compression and also change the oil. it could be contaminated or just cooked from the heat!

 

well i checked the oil and it looks really good. Its less than 50 miles old. I drove it again and as soon as it warmed up it seemed to run noticeably better but not fully though.After driving it a while she started doing the same thing then also started to slightly over heat. I Drove it home and checked the coolant but it was full so ima change the thermostat. Maybe when it warmed up the head or gasket warped again or stretched and thats why it did it after a while but not right after it warmed up.IDK

 

Maybe there is an air bubble in your coolant? Try bleeding the coolant.

 

well i have the same car and one day i was going to work sitting in trafic and the car overheat but as soon as i started to drive it was fine, a very common problem for honda around 80000 miles the thermostat stuch close causing the engine to overheat. the best way to blead civic is let the car idle open the rad cap also on the thermostat housing there is a bleading nipple there crack it open and that will ensure all the air is out.