We just came back from a 400 mile round trip in our 98 Tahoe
6.5TD (NYC area through the Pocono Mountains in PA to
Binghamton NY, then back). Before we hit the road, I had
just changed the oil/oil filter, diesel fuel filter and
lubed the joints. I used Shell Rotella HD 30 SAE, added a
pint of Lucas engine oil honey, a large (V-8) can of Restore
(thanks for the suggestion) and an 8 oz bottle of Tufoil
(used it before on our 86 Sub 6.2 NA with slight
improvement, went from 25 to 26 mpg). Except for the
Restore and Tufoil, I've pretty much stuck with the Lucas
and either HD 30 SAE or 15W40 (thinking of switching to
synthetic after this experience).
Here's the kicker: the engine now is SO MUCH QUIETER, even
when you pop the hood open. The standard noise coming from
the bottom end is slightly less but the change is still
noticeable. It used to hurt my ears leaning over the
running engine but I actually had a cell phone conversation
with the hood up and me looking into the engine compartment.
This was at a McD's 45 miles into the outbound trip. The
interior noise from the engine was also significantly
reduced 'coz the wife and 5 year old boy mentioned it.
I wish I had a decibel meter handy before and after the oil
change to get qualitative data on the engine noise decrease.
I topped up after McD's and, again, when we returned: 357
miles and just over 16 gallons, about 22.25 mpg, doing 65-70
mph (1800 to 2000 rpm where 1850 is max torque). I usually
get 22 mpg on straight level ground doing 63 mpg (right on
1850 rpm). There definitely was a mileage improvement -- we
were 3/4 loaded on the return trip. The engine ran smooth
and accelerated like a 350 gasser. Too early to tell if the
oil consumption will improve (usually down one and a half
quarts between oil changes). Got 166k miles on the truck.
No snake oil claims, just plain old first hand experience.
Don't know if its from the Restore or Tufoil or both, but
I've got me a new quieter truck it seems. Will now do same
for 86 Sub.