I run Amsoil 15w40 synthetic oil with a Amsoil absolute efficiency oil filter in my truck. I was told by Amsoil that with that oil and filter there is a 25,000 mile/1 year oil change intervals. They also conducted a test on big rigs that ran 60,000 miles over the road and had a oil sample sent out to the lab. The lab test showed that the oil was good for another 30,000 miles no problem. They are running Dual bypass filters and change the filters every 30,000 miles but using the same oil. Just goes to show you that the stuff does work and is worth the money. 100 dollar oil change, and no crawlin under the truck in the winter out in the cold. Once a year and check it normally for any burn-off.