Hello just joined and this is my first post.

About a month ago I bought a used Civic 2005 SI 4 door with 130K

Car runs beautifully but I checked the radiator level a few days ago and it was missing about a cup of coolant so I topped it off.

Coolant reservoir was still at Max.

I have read many posts on the 2005 radiator cap problems so I went to the Honda dealer and got a genuine radiator cap and replaced it.

Has anyone else had similar problems with their 2005 civic ?

 

did you check the coolant reservoir when the car was hot or cold ???

 

I measured when it was cold.

The reservoir was still at max but the radiator needed coolant.

 

the max line is for when the car is at operating temperature so it would be on max when the car is hot and the low line is for when the engine is cold. the radiator cap regulates the fluid when hot or cold so a faulty cap would cause issues with fluid levels in the overflow tank.

 

Well I got the original cap from the Honda dealer and the radiator is still low when cold and I need to add coolant to the radiator directly on a weekly basis.

No overheating and The reservoir level did not change. .

 

try flushing the cooling system there mite be build up then purging air out of the cooling system if that doesn't work then you either have a leak or it could possibly be a bad head gaskit. does your engine oil or oil cap have any milky white substance in it ???