Disclaimer: I find this topic repetitive, but I'm as guilty as the next guy, because I cannot turn away from a train wreck about to happen, so read the following with a grain of salt if you're so inclined.
"Marketing mumbojumbo isn't going to help anyone here. What are the technical differences between these two oils?"
I'll be the first to admit that I don't have access to, or knowledge of, the technical data to be able to explain the difference, if you'll admit that there are a lot of folks who wouldn't understand it anyway.
Let me give you some background. My first "real" exposure to the world of chemistry in a business sense was cutting coolant for machining operations. I only got into lubricants after I changed jobs within my first company (Ford). But what I learned about cutting coolants is that there is a VERY diverse, specific world out there. There are times when multiple products will fit the same application, and there are times when only one product will satisfy criteria. Most often, there is a compromise of many attributes considered, and the "best" is the one with the most pro's and the least con's.
So, to the topic of Mobil 1 diesel oils ...
Perhaps (and I'm just spit-balling here) Exxon-Mobil has actually done some marketing research, teamed up with their product engineering teams, and produced lubes specific to the best intent of the target audience?
I find it interesting (or perhaps nausiating) that we see folks who would argue the merits of these nuances when they have no intent of capitalizing upon the benefits. Very few of our memebers actually run heavy OTR fleet operations, (yes, there are a couple). Most of these guys are intersted in the "best" oil for their Ram or Superduty. And while they can spell "best", they cannot accurately define "best".
TDT is aimed at the light-duty truck folks; Dodge/Cummins, PSD, Dmax, etc. These folks typically don't do extended OCIs, and have (relatively) small sumps, comparitively speaking. I don't know that the "needs" of these engines is the same as some 12L, 1300 rpm ,I-6 pulling 80k pounds. So, there are some product variations based upon API cert that are application specific. They (Mobil) are taking into account sump size, OCI duration, base stock, soot loading, etc, etc, etc. Maximum ash content. Minimum Sulphur content. Blah, blah, blah. Yada, yada, yada. THIS IS ABOUT PRODUCTS BEING MARKETED TO SPECIFIC TARGETED GROUPS; THE CONTENTS OF THE PROUDCT ARE UNIQUE TO THE APPLICATIONS.
Why cannot people accept that there are different products for different markets? I realize that it matters to some people that TDT is not the "same" as (at least one of) the Delvac 1 products. There is a fairly broad TBN range in those products Charlie listed, but that means diddly-squat when your propensity to OCI is 5k miles! Heck - most people OCI WAAAAAAAAAAAAAAAAAAAYYYYYYYYYYYYYYYY before the synthetic is used up anyway. Where is the merit of a debate of what's "best oil" when there is no intent to utilize the full capability of the lubricant?
I challenge anyone to show me where TDT has failed and Delvac 1 would have succeeded, as long as they used the products for the correct application.
Charlie often does an excellent job of explaining the small differences between oil certs, and yet it becomes lost in the translation because many people cannot walk away from their concept of there being "one best oil", as if it were a broad paintbrush that could cover everything. Or conversely, they want to believe that there is one identical oil marketed seven different ways.
You have a CAT/Challenger track machine that requires a specific oil? Better use a specified lube. Got a two-cylinder Kubota generator that calls for a specific lube? Use a fluid meeting that criteria. Needing an oil for a Dmax or Ram? Find one that meets the OEM specs.
Mobil has seen fit to offer specific products unique enough to merit consideration across a broad range of OEM equipment. Why must people lust after the grass on the other side, especially when they have no intent of using the fluid to it's full capability anyway?
Oh - I forgot, we're BITOGERS; that's why.