Honda Civic Owner's Manual page 199

If the reserve tank is completely
empty, you should also check the
coolant level in the radiator.
Removing the radiator cap
while the engine is hot can
cause the coolant to spray out,
seriously scalding you.
Always let the engine and
radiator cool down before
removing the radiator cap.
RADIATOR CAP
1. Make sure the engine and radiator
are cool.
2. Relieve any pressure in the cooling
system by turning the radiator cap
counterclockwise, without
pressing down.
3. Remove the radiator cap by
pushing down and turning
counterclockwise.
Engine Coolant
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.
Pour coolant into the reserve tank.
6.
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.
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