rust is always the killer of all things good and holy - what year is your ranger? That 4.0's gone through alot of changes. If it's a 2nd or 3rd gen, you've got a high torque dual overhead cam 4.0 that Ford used in the Aerostars so they'll be descent on gas. My ranger has a 2.3 in it(an engine I didn't even know Ford offered for 1st gen ranger) and probably gets a bit more mpg but not by much.