Hitachi ZAXIS 450LC-3 Operator's Manual page 320

5. When adding hydraulic oil, always use the same brand of
oil; do not mix brands of oil. As the machine is filled with
Super EX 46HN when it is shipped from the factory, use
it as a general rule. When selecting to use another brand
of oil listed in the table "Brand names of recommended
hydraulic oil", be sure to completely replace the oil in the
system.
6. Do not use hydraulic oils other than those listed in the
table "Brand names of recommended hydraulic oil".
7. Never run the engine without oil in the hydraulic oil tank.
MAINTENANCE
7-50