PING: Jonathan / Quieter Diesel

Hello Jonathan,
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.
Regards, Franko
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Franko,
Glad to see that you noticed an improvement. My old '95 C1500 with the 6.5L turbo diesel was by far the quietest diesel I've ever owned or driven, and I typically attributed that to the indirect injection and pre-combustion chambers that GM used on this design. In fact, that 6.5L was quieter without mufflers (it only had a catalytic converter, and I had a dual cat-back straight exhaust installed) than my friends' Ford and Dodge trucks WITH mufflers.
When I started using the Restore, I initially didn't notice any change in oil consumption or oil color until about 3 oil changes - it's a very gradual process. One thing about that motor is that (before I started using Restore) when I changed the oil I could drive it around the block and it would be black again. By the time I traded it in, the oil would darken by the time for the next change but still have a gold sheen to it, and my oil consumption dropped significantly between changes from roughly 1qt/1000 miles down to 1qt/3000 miles or so. I just hope that the next guy who bought that truck continues on with it.
Cheers - Jonathan

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