Honda Civic 2021 Owner's Manual page 533

uuMaintenance Under the HooduEngine Coolant
■
Adding the Coolant
1.5 L engine models
Reserve Tank
Cap
2.0 L engine models
Reserve Tank
Cap
532
1. Make sure the engine and radiator are
cool.
2. Turn the reserve tank cap 1/8 turn counter-
clockwise and relieve any pressure in the
cooling system.
3. Push down and turn the reserve tank cap
counter-clockwise to remove it.
4. Pour coolant into the reserve tank until it
reaches the MAX mark.
5. Put the reserve tank cap back on, and
tighten it fully.
1Engine Coolant
Do not add rust inhibitors or other additives to your
vehicle's cooling system. They may not be compatible
with the coolant or with the engine components.
1Adding the Coolant
NOTICE
Pour the fluid slowly and carefully so you do not spill
any. Clean up any spills immediately; they can
damage components in the engine compartment.