ls1 overheating.
OP seems to be saying: the tube coming from radiator neck and going into the overflow reservoir...
OP can you confirm this...?
The radiator cap will overflow out into the overflow if the pressure builds too high in the system.
The overflow is not quite anything except a place to catch all the fluid that may come out.. so it doesnt go onto the ground/into the environment around you
if the overflow pipe leaks (which is what we think the OP said) then air will be drawn in instead of coolant.






