Honda BF20A-BF25A, BF25D-BF30D Outboard Motors Shop Manual., Page 249Get this manual
NOTE: No problem if the overheat indicator comes on when restarting the engine after hot soak at high temperature but goes off after idling for few minutes Yes
Remove the blockageNo Start the engine and check whether the cooling water constantly flows through the check port with the engine idling, Does the water constantly flow through the check port?
Clogged or damaged water tube Clogged check port
down the engineDoes the overheat indicator go off?
a System is OK (Overheat problem was removed)
Check the thermostat Normal