I am in my mid 60's and have always been a very high mileage driver in my career and with my small 40 acre farm. I have put 300K on multiple diesels. Two of them VW tdi's which called for synthetic oil only.
I have had excellence results with group 5 synthetic oils running 10K oil changes on diesel and gas engines. I occasionally back that up with oil analysis until I am sure I am not pushing the oil to far. I will admit I am doing this 1/2 for convenience sake to cut down on doing oil changes every 3 weeks.
I am running 15W40
Amsoil synthetic in my Ram CTD right now. I'm not paying the prices ar this link because I am an Amsoil dealer for my own use just because I have enough equipment it makes it worth while.
Do a little reading on synthetics oils some are group 3 which aren't that much better the standard dino oils. The best are the group 5 oils and they are of much better quality with better additive packages. Mobil (Delvac), Shell and Cat also have some good quality synthetic oils.
If your looking for big fuel mileage gains, I don't think you will ever see it. At least I haven't anyway.
