Poor gas milage ?

[Pops]

I recently briefly used a 15/40 HD Diesel oil with less VI @ 100c than a PCMO 20/50 and noticed a marked difference in gas milaege on the hiway. The HD oil using more gas . About 1.5 miles per gallon less . Same gas brand. Same trips. Same temperature outside . Is the cleaners in the HD oils doing more cleaning that lubricating verses the 20/50 car oil causing the milaege to drop?

 

[jason07-1zzfe]

Apparantly certain HDD oils do not have FM, whereas most (all?) PCMO do. Maybe that is the reason?

 

[MolaKule]

Unless the oil is Delvac 1, in which the esters and PAO base oils are the FM's.