Originally Posted by bulwnkl
Keep in mind that diesel oils need not be (and thus almost never are) friction-modified like gasoline oils are. That means, even if everything else is the same, the non-diesel oil will be 'slicker' so to speak. One might possibly notice this in how free-revving the engine is, or in slightly better mpg. Again, this is with everything else being the same (viscosity, bases, protection levels, etc.). So, if you can get the viscosity you want in a non-diesel oil, you get other benefits.
Another speculation that I'll make is that folks that push their cars harder are less concerned with fuel economy.
I do wonder what the actual difference is though between mpg's with say Amsoil 10W30, 5W40 Diesel and 5W40 Euro. On a recent trip from NJ to SC, my fuel economy varied by nearly 5 mpg's depending how fast I drove and how much weight I was carrying.
It's a good point that if you don't need
a Diesel 5W40 that you will get benefits from other oils. I'm pretty sure that Amsoil would even email your the amount of additives in their oils. They list the amount of phosphorous and zinc in their heavier duty oils here: http://www.amsoil.com/dealer/techser...lat_Tappet.pdf
I would assume that the levels in the diesel 5W40 are less since has similar specs to a CJ-4 oil.