Honda Civic Service Manual: Engine Cooling

Engine

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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. How the System Activates
The system becomes ready to start searching for lane markings when all the following conditions are met:  The vehicle is traveling between about 45 and 90 mph (72 and 145 km/h).  The vehicle is on a straight or slightly curved road.  The turn signals are off.  The b ...