I just got a new to me diesel truck for trips with the family. I noticed on the oil change sticker that the last owner just had the oil changed 500 miles ago. I was going to change it when I got it home but decided to give the repair shop on the sticker a call. I acted like I was going to come in for an oil change and asked how much and what brand oil they used in diesel trucks. They use only 15w40 rotella t so I was happy with that and decided to wait untill time to service it. The machanic also told me that the truck I bought was always serviced there and he knew the owner. I will most likely keep on using the rotella.