Honda 2003 Civic Hybrid Owner's Manual page 194

Engine Oil
The oil's viscosity or weight is
provided on the container's label.
Select the oil for your vehicle
according to this chart.
Ambient Temperature
196
Maintenance
A very low-viscosity, fuel-efficient
0W-20 oil is the preferred engine
lubricant for your Civic Hybrid. This
special oil is formulated to help your
engine use less fuel. It is available at
your Honda dealer. A 5W-20 oil may
be used if 0W-20 is not available.
Synthetic Oil
You may use a synthetic motor oil if
it meets the same requirements
given for a conventional motor oil: it
displays the API Certification Seal,
and it is the proper weight as shown
on the chart. When using synthetic
oil, you must follow the oil and filter
change intervals given in the
maintenance schedule.
Additives
Your Honda does not require any oil
additives. Additives may adversely
affect your engine's or transmission's
performance and durability.