03 Grand Marquis coolant leak rear of engine block ...heater hose appears to be in good condition and no visible leaks. That being said I know that hose travels under the intake manifold over the block. Is it possible hose is broken in that channel?
There is a pipe that runs under the intake that has an o-ring seal at the back of the water pump. It happens but most common is the plastic nipple at the right rear of the intake manifold (it points straight up and the hose goes from the manifold to the heater core) We've had to change many manifolds now because of this failure. I changed an Intake tonight because the seal between the plastic Intake and the aluminum water passage across the front leaked badly. Hang on to your wallet - these intakes are quite expensive from Ford ($400) - we have to run OEM parts because we service active Police Interceptors but you may be able to pick one up on E-bay for a lot less.
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