for what it's worth..
I've been doing personal research on synthetics for years, and I just happened to read a lab report comparison today, Amsoil 3000 (5w-30) vs the best non-synthetics. It said that Rotella 15w-40 is the best of the non-synthetics, overall. I'm not going to quote numbers, but it was above the others in all tested categories, with Delo 400 15w-40 next best. I used Delo until I changed to the Amsoil full flow system and the 3000 series 5w-30, and it seemed to do fine. I changed every 4k miles, and I push my CTD pretty hard. If I was going to baby it I would have bought a F-150!! The main reasons I went to the Amsoil were that our trucks have turbos, and non-synthetics will 'coke up' in the turbo alot quicker, and at significantly lower temps than Amsoil. Also I run hard and long, and sometimes if I'm on a trip (towing) it just isn't practical to get an oil change when there's a trailer hooked on the back. Amsoil has an analysis program and it may not be a whole lot cheaper, but it is a little cheaper, than changing the Delo or Rotella, and the filter, at 4k miles, but it sure does save the time and hassle. I do it myself, so by the time I go to Wal-Mart for the oil and filter, which they always had on the shelf and Auto Zone had the oil but not the filter (FRAM), get back home, crawl under it, open the drain after I find a 3 gallon pan flat enough to slide under the truck (a kitty litter pan is the only thing I found that works, other than a $50 "professional" metal pan), drain the oil, remove the filter, fill the new filter with new oil and screw it into place, refill the crankcase, then I have to fill 3 empty jugs with used oil and drive to Auto Zone to dump it in their recycling tank, etc. , etc. I pull 4,000 miles in a month, give or take a week, so if I kept doing what I was doing I spent half of my spare time changing oil. The facts are, synthetics work, they last longer and lubricate better, they are waaay better in a turbocharged engine, they enhance fuel mileage and offer a small percentage of power increase, due to less internal friction, and if you get a regular analysis, it is less costly to maintain your diesel workhorse in the long run. I do admit it might not be for everyone. If you run about 1000 miles a month, the average for most personal use trucks, I can see where it would take longer for you to realize a savings than it does for me. I get an analysis, change filters on a regular basis, and use the same oil for 25 thousand miles, maybe longer if the analysis indicates it. I know of one driver that has 50,000 miles on the same oil, with just filter changes and analysis so far. I know, it's hard to believe. On the other hand, I don't know anyone that takes better maintenance care of their truck than I do, and if it works for me, it must be pretty good stuff. There might be someone that takes better care of their rig than me. I just haven't ever met him! In summary, whether or not Amsoil is for you is a personal decision, based on your driving, monthly mileage driven, if you tow frequently or none at all, and how you feel about down time and maintenance. If someone has a CTD and doesn't tow or carry a heavy load with it, they would be better off with a 1500 or a--I hate saying this--F 150. In case I haven't made it plain, I'm talking about the Amsoil extended drain interval system, with 2 filters and routine analysis, not just driving for umpteen thousand miles on the same oil and filter. Ok, I'm getting off the soapbox now. I thought I'd throw some opinions, experience, and optional ideas into the discussion. I fully expect to get a million miles from my CTD, no BS, and the oil program I'm using will go a long way towards that goal. I know other drivers that have done it, so I know it is possible.
Attention: TDR Forum Junkies 
:{ 
