Honda 2007 Civic GX Online Reference Owner's Manual page 233

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Engine Coolant
RADIATOR CAP
U.S. Si
3. Remove the radiator cap by
pushing down and turning
counterclockwise.
230
RESERVE TANK
Except U.S. Si
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 any.
Clean up any spill immediately; it
could damage components in the
engine compartment.
5. Put the radiator cap back on, and
tighten it fully.
RESERVE TANK
U.S. Si
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 vehicle's
cooling system. They may not be
compatible with the coolant or
engine components.