The reservoir cap contains 2 valves, one to release air to maintain the correct operating pressure,
and the other allows air to enter the reservoir as the pressure drops during cooling, this could hiss.
Look for pinkish white powdery residue near cooling system connections, on the 1.8 the CTS flange is common.
and the other allows air to enter the reservoir as the pressure drops during cooling, this could hiss.
Look for pinkish white powdery residue near cooling system connections, on the 1.8 the CTS flange is common.