Sounds like either the
thermostat is not opening and needs replacement
or head gasket is bad
If the engine coolant reservoir has a thread on cap , that is your pressure cap / " radiator cap "
too much water added the overflow is designed to let out water.onece the radiator reaches the required pressure,the excess water is exhausted thru the overflow
You can blow into it. that hose will only really be open to the radiator when too much pressure has built up and your radiator cap releases pressure into the overflow. All other times the tubes access to the radiator is blocked by a properly functioning radiator cap.
Sounds like you need a new radiator cap, you can get the cap tested to see if it is holding the rated pressure.
There is no actual "radiator cap" due to the fact you have DexCool and an overflow with a pressure vent cap on it already. That is where you fill it up anyway....
Bad radiator fluid.
The pressure from the radiator is pushing out through the overflow canister. Probably solved with new radiator cap but could be an indication of head gasket problems if pressure gets too high.
Heat from the engine causes liquid to expand. It used to overflow onto the ground if it caused enough pressure to open the radiator cap. The overflow tanks were installed to automatically catch and return the coolant to the cooling system.
Filling the overflow to the correct level will suffice as the radiator will draw out what it needs.
the overflow res. cap is the radiator cap on the 97 cavalier
If you mean the cap for a car radiator the water will heat up and overflow. The radiator/cooling system requires a pressure of usually around 16 lbs which is what the radiator cap provides in stopping water from overflowing.
coolant overfilled? thermostat not opening allowing pressure to build-up? --------------- Please test the radiator cap with a pressure tester. Also, look for a cracked head or bad head gasket.