Honda FourTrax Rancher TRX420TM1 2020 Owner's Manual page 149

Coolant Replacement
Refer to Safety Precautions on page 103.
Coolant should be replaced by your dealer, unless you have the
proper tools and service data, and are mechanically qualified. Refer
to the official Honda Service Manual (page 242).
WARNING
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.
To properly dispose of drained coolant, refer to You & the
Environment, page 202.
NOTICE
Improper disposal of drained fluids is harmful to the environment.
WARNING
3
Coolant
Servicing Your Honda 139