2000 Explorer, 4.0L push rod engine. 165,000 miles Water is leaking from the back side of the engine. Passengers side. It leaks without the engine running. If I put water into the raditor after it stops leaking it will start again until it drains down. What is the most likely cause? Head gasket? Intake manifold gasket? Is there a sensor back there? Core plug? I've removed the air plenium already but still can't see back there. Is there a usual problem that causes this? The engine runs fine, no smoke, good power, I obviously can't run it long before it will over heat. This just started all of a sudden. Thanks for all help and suggestions.