Shift Schedule Guidancew

[wmpbauer]

We bought a 2011 Phaeton 40QTH and simply love living in the coach. ISC8.3/DEF/Allison 3000/on FCCC XC-R.

Driving costs though are a very real concern, and we exercise careful control of our weight, don't carry a lot or water and never keep our DEF over half full. We're up to @7500 miles and are experiencing average fuel mileage calculated at 6.78 mpg calculated on our total miles and total fuel without adjusting for genset use which is under 200 hours. I didn't use the economy mode until after 5000 miles for engine break-in purposes, and I was pretty careful about speed variance over the first 5K miles.

As I try to become more educated, I've been reading about Performance, Economy, and LBSS settings on the Allison 3000 transmission. None of the owner's manuals really provide much guidance on when to choose which mode setting. Should you just put it on economy and forget it to maximize fuel economy? Under what conditions should you switch to performance or load-based shift schedules? It appears that if I begin to experience elevated engine operating temps, I should increase my RPM's to boost cooling, but that is the only real guidance on this issue (other than weight and distribution) I've gleaned from reading all the manuals cover to cover.

an anyone provide some general operating guidelines as to when to use a different shift schedule?

[Mr_D]

The only thing economy mode does is change the rpm of shift points under full or near full throttle. I have mine on most of the time, but the only real change is in rolling hills where the trans downshifts and upshifts (hunting) a lot. It allows the engine to pull down to max torque rpm before downshifting. I have mine on most of the time.

[Steve Ownby]

Yes, that is below average mpg for an ISC. The mode program will not make very much difference and I no longer try to use it. If you want to maximize economy, especially on the flat to slightly rolling highways of Florida, you should have a target speed just above The shift into 6th gear. On rolling hills, let your speed increase some on the down leg and fall off on the up leg. You should not have to worry about temps unless you are on a grade for number of miles. You are correct that if your temps get much over 200-210 them a downshift to increase rpm is in order. On long climbs of 6% or greater, maximum fun and best for temps is just below governed rpm.

If you are driving conservatively, after you adjust for generator usage, that ISC should be capable of better than 8 mpg in normal driving conditions. If you continue to be dissatisfied a trip to a Cummins dealer with a Dyno for a test run could see if you have any issues under load. It's unlikely but you could have a fuel leak somewhere. If so you should see some evidence under the coach.

[Barlow46]

What was your total fuel used for the 7500 miles and what is your fuel tank capacity? Your results could be skewed somewhat depending on how level you were when you filled up. Also, the longer you last on a run results in better mileage, especially on the interstate. How much was interstate, what was your average speed, how often did you take a rest break or if not all interstate, how much 2 lane stop and go running did you do in that 7500. I think if you continue to keep good records using hand calculations only when filling up, you may find after another 7500 miles that your mileage figures may increase. Also, your generator running 200 hrs. burned at least .5gal per hour at 1/2 to 3/4 load depending on the size and how many a/c's were running during that 200 hrs. That would account for at least 100 gallons of fuel to figure in the equation. So many factors involved in fuel mileage.........

[a k]

You might get 8 mpg if you never go over 55 MPH. 40 ft'r with an ISC? come on.

[JimM68]

get just slightly over 7mpg, in a 40 foot ISC, towing.
I run 65 mph, use the cruise control a lot, never use economy mode, and pretty much don't think about fuel, exept when it's time to buy more.

I've heard going slower will get slightly better mpg, never managed to slow down long enough to prove it..
I've also heard that many who claim 8 or more mpg just might be somewhat inaccurate.

[powerboatr]

I run between 7.5 and 7.9 in our ISC equipped NON DEF 40 footer and we weigh right at 30-32k depending on what we feel like taking with us. This is in Texas with rolling hills of Austin up to the flat land of the piney woods,up to Arkansas and back.
this mpg doesn't change with the truck out back on the trailer either. I run 65-67


I am curious why you only run 1/2 tank of def? do you carry extra in the basement?

i would second the accurate fuel fill up a few times to get a real world mpg
also what does your dash info bar tell you? my f/l info bar has been dead on for us.


anywho
fill her up to the neck....do it slow and get a real full tank.
then drive to burn up at least a 1/2 tank then fill her up right to the neck again and use that for your actually fuel usage
during this run...dont use the genny
then the next run use it the entire 1/2 tank and compare readings

for us running the genny makes me drop to 7.0-7.5 but not always.....
I find WIND is the biggest killer of mpg, so 65-67 is pretty much the speed unless we just have to get somewhere in a hurry

i think with your low mileage.....it will come up some as she breaks in.

[Coma]

After 10k miles I am at 8.5mpg. I run 65~67. We run the Generator when its hot and the Aquahot when its cold. Thats included in the 8.5. I use the Econ mode. I weigh 32k down the road. In FL I run Econ all the time. I will switch out of Econ on the steeper grades based on speed. On my gearing, it will pull down to ~55 before a down shift. I don't like to let my speed vary that much, so if it varies more than about 5mph I turn econ mode off. You should experiment to find what works best for you.

x2 on it will improve as it breaks in. My three previous light truck diesels didn't really break in till about 30k miles. Give it some time and enjoy the ride!