Honda 2003 Civic Coupe Owner's Manual page 209

Cooling System
RADIATOR CAP
2. Turn the radiator cap counter-
clockwise, without pressing down
on it, until it stops. This relieves
any pressure remaining in the
cooling system.
3. Remove the radiator cap by
pushing down and turning
counterclockwise.
208
Maintenance
RESERVE TANK
4. The coolant level should be up to
the base of the filler neck. Add
coolant if it is low.
Pour the coolant slowly and
carefully so you do not spill. Clean
up any spills immediately. Spilled
coolant could damage components
in the engine compartment.
Put the radiator cap back on.
5.
Tighten it fully.
6. Pour coolant into the reserve tank.
Fill it to halfway between the MAX
and MIN marks. Put the cap back
on the reserve tank.
Do not add any rust inhibitors or
other additives to your car's cooling
system. They may not be compatible
with the coolant or engine compo-
nents.