Honda BIG RED 2009 Owner's Manual page 116

Coolant
Radiator Core
Refer to Safety Precautions on page 69.
Check the air passages for clogging or damage. Remove insects, mud,
or any obstruction with low water pressure. Have the radiator checked
by your Honda dealer if more than 20% of the radiator surface air flow
is restricted.
Clean the radiator core after driving your Honda MUV in mud.
To clean the radiator core:
1. Open the front hood (page 82).
2. Wash the radiator core with low water pressure.
Do not apply pressured water directly to the radiator core. The
pressured water can damage the radiator core fins.
Servicing Your Honda 107