Originally Posted By: dnewton3
You need to view this from a pragmatic perspective.
Oils are asked to do many tasks:
1) lubricate; reduce friction/contact wear
2) cool via thermal transfer
3) clean/maintain cleanliness
4) assist in efficiency via reduced pumping loss
While the 6.7LPSD is fairly new, I've not seen any evidence of major wear factors so far in UOA evidence. I think it may be too soon to speak of sludge issues, as there may not be enough data yet one way or another.
In FL, there is no need for synthetics unless you're going to greatly extend your OCIs well past the OEM spec, or unless you plan to venture far, far north in the cold of winter.
Any decent 10w-30 dino HDEO (there are several, but are often hard to come by at times) will do a great job, even when towing.
There is nothing "wrong" with using a 15w-40, but it will have an effect on your fuel economy. Since you only plan to tow occasionally, the benefit of lighter grade for daily driving would outweigh any perceived risk of the towing issues.
I would suggest any major brand of 10w-30 HDEO you can find at the best cost that makes you happy. T5 is an excellent choice because it is widely available at nearly any WallyWorld for a good price. But if you can find/negotiate for 10w-30 HDEO dino at your favorite autoparts store, I'd not turn away from that option either.
I personally have used Rotella TP dino 10w-30 for a few years now and had excellent protection and service from it year round; cold IN winters and heat-soaked travel-trailer trips in the Southwest not withstanding.
Most of our fleet 6.4s and 6.7s run the 10w30 TP and the oldest 6.4 has over 100k of strictly pulling and havent had a problem yet. I wont get into the OCI and lube management because no matter what I've tried, 3-5k is it because it is "cheap insurance", I could easily reduce our lube cost by 50% but I'm not in change of maintenance, just DOT compliance.