If the vehicle previously got hot enough, it could be that you have developed a cylinder head or head gasket issue. Not necessarily common in the 3.0 Nissan / Mercury Villager engine, but definitely possible. See if the coolant reservoir smells of exhaust fumes. This is a good unofficial unscientific way of checking for a head issue.
I think you have a classic case of blown head gaskets. The least that would require is replacing the head gaskets. I'd say, get the car to a Ford specialist, tow it because if you drive it you will get it hot again and risk causing more damage. Try pulling the oil dipstick. If the oil is gooey and looks like a chocolate milkshake, there's coolant in the oil and that's usually caused by badly blown head gaskets. here's a directory link for you: http://repairpal.com/directory?address=76401&car_brand_names=Mercury