Yamaha XZ550RJ 1982 Owner's Manual page 139

1. Drain bolt I. Bouton de vidange 1. Perno de drenaje
-127-
b. RADIATOR
The coolant in the radiator can not be
drained from the water pump cover
drain. To drain the radiator, proceed as
follows:
1) Remove the screws (two) securing
the thermostatic valve cover and re-
move the cover. The coolant rush
out.
2) Thoroughly flush the cooling system
with clean tap water .