Porsche 911 GT3R 2010 Technical Manual page 18

3.5.4. Filling the cooling system
A quick-release coupling is integrated in the area of the expansion tank.
The water system can be filled and bled quickly and safely via this
coupling – after an engine change for example.
Quick-release coupling
Attention: When the water system has reached its operating
temperature, the expansion tank cap should under no
circumstances be opened and the pressure released. Since the
operating temperature has already been achieved the water
pressure cannot be built up again. This system pressure is
necessary to increase the coolant boiling point.
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