Originally Posted by bluesubie
I'm not JnJ, but I'll speculate.
Diesel oils, in general, have a higher level of anti-wear additives like zinc and phosphorous. That's why so many are switching to Rotella. Amsoil's 5W40 is actually on the thin of being a 40 weight, while the diesel oil has a thicker viscosity when hot. The diesel oil also has a higher High Temp High Shear.
Compare viscosity at 100C and HTHS:
Amsoil Diesel 5W40
Amsoil Euro 5W40
Dennis your speculation was spot on...
What we have also been doing is testing in various cars some of the different oils... I hope to have some numbers in a a month or so to post up. We firmly believe in real world evaluations. So we try and do it ourselves.
To be honest, we have used ASL 5w 30 then switched to the diesel 5 w 30 when we first got our WRX wagon. After comparing samples (I would have to look for the paperwork, it has been about two years) and the specs of the Euro 5 w 40. We made the decision to use the Euro 5 w40. It was less expensive than the diesel 5 w30 at the time... However, with us turning up the wick on the wagon we will feel better using the Diesel 5 w40.
A preferance, not a Amsoil influneced one.