2004 ISL

[pnordan]

We have '04 Tradition with ISL(370) Cummins, F/L chassis(chassis date July '03). We are about 3900 miles into our Alaska trip with an MPG average of 6.3. In the C/G I met a couple with an '05 Tradition, same engine but on a Spartan chassis. He "says" he averaged 8.5 on the trip up from California.
Was there an engine mode after my chassis was built that would account for the difference in MPG? Should I contact Cummins to ask this question? At $1.42 liter in Canada it adds up.

[pusherpilot]

On our 04 Imperial the Aladdin system keeps track of the stats. I just went out and checked, the coach, since its born on date has traveled 101945 miles at an average of 50.6 mph and average fuel mileage of 7.7. It also keeps individual stats for a trip setup on the computer. It saves the last 10 trips and provides the same info as I mentioned above for each leg. It's an ISL 400, weighs in at around 33k lbs without tow which adds about 4500 lbs. I reset the Aladdin on a new trip when I fill the tank and use the fuel consumption feature to tell me when I need to stop for fuel. The fuel gauge is useless and has failed several times and I'm so used to not using it that I'll not fix it again.
As an OBTW, I've logged a few trips over the central plains where a tail wind had allowed me to travel at 70mph ans still see an average of 9.5+ avg mpg. Wifey and the fuel fund both pray for tailwinds!!
Ron

[randallb]

You climbed through the Appalachians, across the plains (WINDY) and over the Rockies/Cascades,etc and you expect the same mileage as someone who traveled relatively flat roads (comparatively) to get to the same spot. Go ahead and call Cummins. I am sure the customer service reps need a good laugh. Their days are usually spent dealing with screamers.
Randy

[topflite51]

More likely than not, he has a better calculator than you. If it really matters get a new calculator.:b

[Westenthal]

I have a 400 hp ISL in a 43' coach and I get 6.2 - 6.3 mpg. It doesn't make any difference if I am toeing my F150 or not. This is my 4th coach, second diesel pusher and I have never goten the mileage others claim on any of them. I don't really care what I get since it still is the cheapest form of travel I'm aware of.

[Sully2]

Fishinghat wrote:
You didn't indicate the weight of your coach, but even if you're in the mid 30,000 range, 6.3 mpg is pretty poor. Most ISC/ISL Cummins owners get up into the 8 mpg range, or better. (The ISM and ISX engines are down in the range you're experiencing.)

I beg to differ with you about that!

[DSDP_Don]

pnordan.....There are too many variables to consider here. I have a short 36' with a 400 ISL. It got 8.2 on average for many years. As I got older and retired two years ago, I made some changes and slowed down a little. We now drive at 59-60 mph which on my coach is 1490-1510 rpm. I don't do any jack rabbit starts. I drive mainly with the cruise control, even in light traffic. I don't like the feel of the throttle so I use my SmartWheel and can thumb up or down the speed on the cruise control almost as fast as working the pedal.

Your Grand Cherokee is moderately heavy as a toad. When I enter a freeway ramp and there is room, I reasonably accelerate up to 45-50 mph, turn on the cruise and then thumb up the cruise control one mile an hour every few seconds until I'm at speed.

If I know I'm exiting in a mile or so and again, if there is no traffic, I kill the cruise and get a good coast to the off ramp. All of this helps when towing.

I run a SilverLeaf computer program on my dash and can see my instant mpg's. I will often look at this and adjust my driving habits. Sometimes, one mph slower or even faster can make you get better mileage depending on the situation. If I see the mpg's are picking up because of a downhill grade that is tough to see with the naked eye or I'm getting a favorable wind push, I may bump up the speed a mile or so an hour.

Source Engineering, is a sponsor on here and offers a replacement engine fan for rear radiator coaches. It replaces the fan you could use to fly a Cessna, with something more technologically advanced that gave me a constant .05 mpg increase with identical cooling.

Lastly, you have to average fuel over MANY fill ups and try to fill the coach the same each time. I level my coach with one jack usually when fueling so I get close to the same amount of fuel. It only takes a moment to do so.

On a long trip of 400-500 miles with no huge grades and not towing, I get 9.8-10.3 mpg if I practice all of the above. Towing my 5500 pound truck I lose about one mpg. Short trips locally, not towing, I see about 9.2 - 9.5, too much starting and stopping.

My mileage is always checked against the computer and calculated manually. My wife does the calculations while I fill up and then we compare her results to my computer as I reset the screens.

Our biggest increase in mileage was slowing down from 63-64 mph to 59-60 mph. I recently added the DigiCR computer chip to my ISL. I'm seeing improved mileage, but haven't had a long enough trip to get a good enough calculation to see if it's helping. There is an HP increase, but not a huge feel in the seat of the pants as there was with changing the fan. Will gather more info in 2 weeks with a trip to Utah and some climbing.

This was kind of a long post, but shows many things that can be changed in habits and parts to increase mileage.

[supermod38]

He "says" he averaged 8.5 on the trip up from California.


yup, and i get 18mpg with mine.....................;)

if you want better mileage just do like most others ***LIE***

won't help the pocket book but hey after a while you may even believe it too. heck our politicians do it all the time..................:W

[pnordan]

Just got Wifi again.

Weight is around 33,000 as we are traveling, towing '04 GC around 4,000. My usual speed is 62 - 64 about 1700 rpm locked in 6 gear. Level ground no winds the computer will show 7.5 - 8.5 current mpg. However, from NC to AK we did not have much level ground or zero winds.
I will contact Cummins for some advice.

Thanks

[The_Texan]

60 mph in a 40' with ISL = 8.5 mpg.........68-70 in the same coach on the same road = 7 mpg........Most 38'-40' have equal rear gearing, but if they don't, it takes a heck of a gear difference to make that big of a difference.....Your weight and driving habits are the main contributing factors.

[mgh122]

Check the gearing on each coaches rear axle, that could explain the mileage difference.

[Fishinghat]

You didn't indicate the weight of your coach, but even if you're in the mid 30,000 range, 6.3 mpg is pretty poor. Most ISC/ISL Cummins owners get up into the 8 mpg range, or better. (The ISM and ISX engines are down in the range you're experiencing.)

Tire pressure, speed, weather and a multitude of other factors can influence mpg.

[Fishinghat]

You didn't indicate the weight of your coach, but even if you're in the mid 30,000 range, 6.3 mpg is pretty poor. Most ISC/ISL Cummins owners get up into the 8 mpg range, or better. (The ISM and ISX engines are down in the range you're experiencing.)

[lanerd]

Are both coaches the same size, are the pulling the same weighted toad, does he drive the same speed as you, did he go over the same highways as you????

There are so many different aspects to getting good mpg.

Ron