If the bottle or jug says "SL" in addition to the various diesel qualifiers, it's a "fleet" motor oil and perfectly safe to use in gasoline engines. It won't say "GF-3" simply because of its higher visocisity, nor will it have the API "energy conserving" wording, again, for the same reason, nor will it carry the API "starburst" seal on the front of the bottle or jug. I doubt you'll find much Motorcraft 15W-40 at truckstops either. I have a hunch this weight Motorcraft oil is most often used at Ford dealers as service fill in Ford pickups with the diesel engine option when the owners insist on it. Nothing wrong with it, but the major players and most widely distributed for heavy-duty diesel engine applications are likely the Delo and Rotella formulations always stocked at truckstops.