HDEO oils are now CK-4 lower ash. It's all about emissions and mpg in the trucking world.

These oils also undergo formulation changes that sometimes do NOT result in a designation change--meaning 'we' don't know. I bought over a million gallons of DELO 15w40 and 10w/30 over the years working for Kenworth.

We would be notified of a formulation change so that we could deplete stock prior to arrival of new, but they were always backwards compatible.

Relying on HDEO's for a high zinc content (in a high lift, high spring pressure, flat tappet scenario where hi ZDDP is truly required) may be a dangerous practice. The HDEO industry is changing!