Cadillac 2004 Seville - Manual (Page 294)

1. Park the vehicle on a level surface. You can
remove the coolant surge tank pressure cap
when the cooling system, including the coolant
surge tank pressure cap and upper radiator hose, is
no longer hot. Turn the pressure cap slowly
counterclockwise (left) until it first stops. Do not
press down while turning the pressure cap.
If you hear a hiss, wait for that to stop. A hiss
means there is still some pressure left.
2. Press down on the pressure cap and keep turning it
slowly. Remove the cap.
3. Then fill the coolant surge tank with the proper
mixture, to or above the fill mark at the forward
edge of the surge tank.
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