Originally Posted by Camaro820
so just recently i was giving the engine a little tune. while i had it running and it got to operating temp (160 degrees) i heard a loud clicking coming somewhere between the upper radiator hose, the thermostat, and the heater hose from the intake. after looking closer, i noticed that the upper radiator was collapsing. ok, i replaced it and its still doing the same thing. and also too, when i shut it off, you can hear all of the coolant rush back into the radiator and when i had the cap off to fill it, every time you heard that click, coolant came gushing out of the radiator. would i ultimately fix that if i get a hose with that spring inside?
I'm guessing by your handle this is a Chevy in which case I'd expect the following:
Given that the return hose is always on the pressure side of the pump, it should never experience collapsing while the engine is running. It sounds like the thermostat is installed upside down or there is some other blockage in the return system. This would prevent coolant circulation, except through the heater bypass, while the engine is running. The upper hose would collapse as the pump inlet is applying a suction that can't being sufficiently fed with the bypass. Another possibility is that the if the intake has been off and returned such that the manifold gaskets which may have only an open return stamped hole at one end are installed backwards preventing the return of coolant. Also, some Chevy's source the bypass at the rear of the intake, in which case a normally installed gasket with only a single sided return hole could cut off the bypass which would keep the radiator and upper hose under a negative pressure until the thermostat opens, if the thermostat is installed properly.
When the engine is shut down, the pressure holding the thermostat shut is relieved and it pops open where the radiator that has a partial vacuum in it from the pump's attempts to feed itself will now surge the coolant trapped within the engine into the radiator.
With the cap off the, this coolant will escape because it is very hot and expanded to where its volume is greater than that of the system.
Another possibility is that the if the intake has been off, and returned that the manifold gaskets which may have only an open return stamped hole at one end are installed backwards preventing the return of coolant. this could find a way at shut down to suck coolant back into the return by way of the heater bypass system drawing backwards from the pump return, through the heater core, then back to the common return passage on the intake manifold.
I would expect any of these conditions to be accompanied with an overheat condition, although I could see that so much boiling is taking place within the block that the sensor is trapped in steam instead of coolant, therefore, unable to present reliable temp readings. the clicking sound you heard I suspect is trapped steam escaping explosively inside the cooling jackets.