This type of engine oil is recommended for use in 6.7 Powerstroke engines that are subjected to heavy loads. It can be a turbocharged system or not. The main feature of this oil is that it operates at -4F, and maintains its viscosity at high temperatures. Such oil usually features special additives, which extend the life of the engine, protecting it from premature wear due to increased density. For this reason, you can safely pour 15W-40 in your 6.7 Powerstroke if it's compatible with your old engine oil, without creating any compounds harmful to the engine.