A cracked valley pan cover will allow for engine coolant to come in direct contact with the intake manifold that could negatively affect the temperature of the air and fuel mixture before it enters the combustion chamber. The greatest effect a leaking valley pan cover will have on your engine is when the coolant level drops that negatively affects the cooling system if gone unnoticed by the operator of the vehicle. Because the valley cover is in the center on top of the engine block, no exterior leak will be visible during a routine inspection of the engine compartment.
The valley pan cover is a piece of shaped metal that covers the opening between the top of the engine block on the bottom with the intake manifold on top and the cylinder heads on the sides. This was a common component on many engines years ago, especially when the v-8 engine was first introduced. On many models, this was the barrier to help keep the coolant on the correct path towards the cylinder heads so a constant temperature could be maintained. Today most engines do not have a valley pan cover located on them because the coolant systems have been redesigned in a more efficient manner.
To access a valley pan cover and removal of it requires the air and fuel system to be taken off the top of the engine. This will include both the carburetor and the intake manifold on most models. Once access is made the 8 to 16 mounting bolts should be removed and the valley pan cover removed along with the gasket. The entire gasket has to be removed so a new one can be put into place so it can properly seal this junction. Then the reassembly of the top of the engine in the reverse order it was taken off.