the oil that was used on it before you bought it is best if you can get ahold of that info. if not you need to go to a full synthetic like mobil1. this is because you dont want to go from synthetic to non synthetic oil. engines dont like that esspecialy higher mileage engines. mobil1 is a good oil its all i use in my fords and is readily available at most places you find oil.
Thats what i was thinking. It's a ford dealership near my house so I'lll take it by there and see if they can tell me what kind of oil was used because i dont know