Chevrolet Optra 2004 Owner's Manual page 221

Checking Coolant
The engine coolant surge tank is located in the rear of
the engine compartment on the driver's side. See
Engine Compartment Overview on page 5-12 for more
information on location.
CAUTION:
{
Turning the surge tank pressure cap when the
engine and radiator are hot can allow steam
and scalding liquids to blow out and burn you
badly. Never turn the surge tank pressure
cap — even a little — when the engine and
radiator are hot.
The vehicle must be on a level surface. When your
engine is cold, the coolant level should be between the
MAX (A) and MIN (B) marks on the coolant surge
tank. The level rises at engine operation temperature
and drops again when the engine cools down.
5-23