Honda FourTrax Rancher TRX420FE1 2019 Owner's Manual page 147

Coolant Replacement
Refer to Safety Precautions on page 101.
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 200.
NOTICE
Improper disposal of drained fluids is harmful to the environment.
WARNING
3
Coolant
Servicing Your Honda 137