I'm somewhat of a newbie but I was wondering tonight why diesel engines would require a HDEO. Diesel engines should be easier on oil than gas engines according to my understanding. Diesels run at a lower RPM and I think they run cooler if I'm not mistaken. Also, we all hear of OTR trucks logging hundreds of thousands of miles and some even reach a million. Rarely do I hear of a gas engine making it to 300,000 miles let a alone a million. So why would a diesel engine need a HDEO?