I just changed my brand with the last two oil changes. I didn't go syn, I've been using 15/40 Rotella dino exclusively since new. 120,000 miles at last change, I have noticed that I was losing some oil between changes and I had a few drops in the driveway. I was probably adding two quarts in the 5,000 miles between oil changes. I switched to Valvoline diesel oil 15/40 and didn't have to add any over the 5,000 miles between changes. Don't know why but I am waiting to see if this oil change works out the same. I have thought about switching to syn but couldn't justify the cost, I don't want to go extended mileage between changes.