Chevrolet 2007 Optra Owner's Manual page 270

Checking Coolant
The engine coolant surge tank is located in the rear
of the engine compartment on the driver's side of
the vehicle. See Engine Compartment Overview on
page 258 for more information on location.
270
CAUTION:
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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.
To check the engine coolant, the vehicle must be
on a level surface. When your engine is cold,
the coolant level should be between the
Maximum (A) and Minimum (B) marks on the
coolant surge tank. The level rises at engine
operation temperature and drops again when the
engine cools down.