Many Ford vehicles along with others recommend the use of 5w30 motor oil. On some Ford vehicles, using a higher-viscosity oil can set a DTC (Diagnostic Trouble Code) which is related to the use of wrong oil, contaminated oils, or using the wrong oil filter. Keep your vehicle maintained and use the correct weight, there will be no need for using a higher-viscosity oil.
Assistant Professor, Parts Technology
Alfred State College, Wellsville Campus
Tom Dayton writes:
Jerry - The 4.0L is actually one of the FEW recent Fords that 5W30 is recommended for. The general rule is 5W20 for everything EXCEPT the 2.0 Zetec SVT, the 3.3 Villager engine, 3.4 SHO, 3.9 Lincoln, and the 4.0's. These all take the 5W30 you mentioned. (And of course the diesels running 15W40)