93 Cummins Mileage Update
What a great looking combo!! Took that picture twenty years ago, didn't you?
And some good mpg. 14-16 is the range I found some eight years ago for early HPCR Cummins trucks pulling 28-34' trailers of our type (several brands) where GTW was from 7-11,000-lbs in the South Central U.S.
17-cpm for fuel sure is nice. What does that combination weigh? Avion was doing a nice job of keeping weight low in those years.
FWIW, the following is the MPG checklist:
Alignment performed on both vehicles (don't assume, verify).
Brake drag and bearing pre-set on both vehicles.
Steering slop eliminated on truck (from steering column outwards). This is overlooked in general, but the big truck manufacturers really stay on top of it. 4WD pickups are often terrible in comparison.
And plenty of 2WD not so hot either. I added a sector shaft brace to my last Dodge. Worth it. Usually called a steering shaft brace.
WD adjusted to 100% FALR. Lack of WD hitch is an FE penalty where TW is above 400#.
Closed shoulder commercial truck tires are worth a mpg gain (such as Bridgestone Duravis 500). TT tires, same brand, but r250. Yokohama ry215 with a lighter TT.
Bilstein shocks on truck and polyurethane antiroll bar bushings to replace old rubber. I'd also do body bushings.
And if it hasn't been done, I'd overhaul the trailer suspension with the MOR/ryde legacy rebuild kit as I mentioned in another thread. Consult with them on alignment procedure on that walking beam suspension.
Weigh the TT wheel by wheel before and after suspension overhaul. I'll bet it changes somewhat.
A bed topper not higher or wider than truck cab barely penalizes FE. A tonneau is a benefit, and GM says a half tonneau extending from tailgate to cab about 60% of distance or less is a genuine FE aid as air pressure against tailgate is equalized from both sides.
What's wrong with the cruise control? Mine is "aggressive" on grades, but outstanding on the flats. I've tested and found that setting cruise at 61 instead of 63 offsets that in terms of fuel burn in rolling terrain. Travel time barely changes due to the diesel ability to flatten hills. Ck engine run time against miles. An engine hour meter is a good tool to have.
I realize that the CC on mine and yours is different, but I'd look to make that tool useful. Again, from the big truck world and with pro drivers, CC is a proven aid.
I say all this as, IMO, you are down by 1-1.5 mpg from what it could be. Or, around 10%. Then again, that was a short trip. Figure that around 3-5000 miles that the travel mpg will be at a predictable average.
As to 500k, no, more likely around 350k, the basic design life. The usual tuneup is new injectors at the halfway point, so Id be looking into that soon. Luckily, yours are dirt cheap compared to ours.
The final point of comparison is the percentage penalty in fuel burn. Over the approximate same route and conditions the usual range is 30-40%. The diesel is usually closer to thirty with our type trailer.
This is also a way of checking mechanical condition. Dial in the WD on a scale, nail down tire pressures, and any engine problems will be highlighted where the other conditions as above are already corrected.
A Tekonsha P2 would be the better brake controller unless you can source one of the old Kelsey-Hayes units.