Oldsmobile 1999 Aurora - Manual (Page 261)

yellow blue
6-23
Checking Coolant
The engine coolant surge tank is located on the driver’s
side of the engine compartment.
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.