Honda PIONEER SXS500M 2020 Owner's Manual page 137

Coolant
4. Remove the reserve tank cap.
Always add coolant to the reserve tank. Do not attempt to add
coolant by removing the radiator cap.
UNDER FRONT HOOD
RIGHT FRONT
reserve tank
5. Add coolant to the reserve tank as required to bring the coolant
level to the MAX level mark.
6. After adding coolant, install the reserve tank cap and install the
front hood.
130 Servicing Your Honda
reserve tank cap
MAX
MIN