Honda Civic Service Manual: Engine Cooling

Engine

...

Coolant Replacement (R18A9)

1. Radiator Cap 1. Wait until the engine is cool, then carefully remove the radiator cap. ...

See also:

Honda Civic Owners Manual. Getting Ready to Replace the Flat Tire
Open the trunk floor lid. Take the tool case out of the trunk. Take the jack and wheel nut wrench out of the tool case.  Unscrew the wing bolt, and remove the spacer cone. Then, remove the spare tire. Place a wheel block or rock in front and rear of the whee ...