water leak on 1991 Oldsmobile Cutlass Supreme

I have a water leak at the back of the engine what could it be ?

Asked by for the 1991 Oldsmobile Cutlass Supreme
The way an automotive shop would locate the leak is by removing the radiator cap and attaching an adapter that screws on in place of the radiator cap. Something that looks like a bicycle pump with a pressure gauge attached to it is used to "pump up" pressure to simulate pressure generated when the cooling system is at operating temperature, the leak is then found sometimes it is obviously leaking from a coolant hose or cracked housing, failed gasket or water pump, sometimes the engines cooling system needs to be inspected from below or inspected using a mirror and flash light.
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it could be a number of thing's intake leaking head leaking freeze plug leaking