The new Amsoil 5w-40 is similar to Delvac 1 in terms of high temp, high shear viscosity.... I think it's an excellent choice for high mileage, worn engines that originally called for 5w-30 or 10w-30. I do expect it to be more shear stable than an SAE 0w-40, which really isn't saying much.
The additive chemistry of the Amsoil 5w-40 is more like the Mobil 1, 0w-40, in that it's optimized for high performance gas engines and passenger car diesels. I would NOT recommend this Amsoil 5w-40 for use in HD diesel engines used in plckup trucks. Both the Amsoil 15w-40 and Series 3000, 5w-30 are better suited to those applications.
HT/HS Viscosity @ 150C/302F:
Amsoil 5w-40 -------4.2 Cp
Delvac,5w-40 -------4.1 Cp
Mobil 1, 0w-40 ------3.6 Cp
Amsoil 5w-30--------3.5 Cp
Redline 5w-30-------3.5 Cp
Castrol 0w-30--------3.6 Cp
The Mobil 1, 0w-40 is functionally more like most of the other, top tier 30wt synthetics ....
Tooslick
www.lubedealer.com/Dixie_Synthetics