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Old 05-14-2010, 02:37 PM   #15
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what Is it that I'm doing wrong that it seems that everybody gets better MPG then me and I have some modifications done that is suppose to help with better mpg
Kinda makes one wonder if those modifications are doing what the salesman told you they'd do.
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Old 05-14-2010, 03:01 PM   #16
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If all the mechanical and electronics are working properly, the only thing left is how you drive it.
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Old 05-14-2010, 05:43 PM   #17
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Our 2007 Ellipse 40', 400hp Cummins ISL towing Ford Explorer has gotten between 7.4 and 7.6 mpg since new. It's improved a bit over time but not much. Weight is 30,000lbs and I drive about 62. I can see considerably better mileage at 55 and MUCH worse at 70.

An excellent point was made about density altitude which I hadn't thought of. I've spent the past 5 months going from Calif to North Carolina and really noticed an improvement when I left central Texas. Hmmmm.....
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Old 05-14-2010, 05:59 PM   #18
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Rick, in professional drag racing we are alert to changes in Density Altitude because we have to change the amount of fuel to match it. It makes a big difference to our performance. One weekend at a track in southern Louisiana we had a Density Altitude of minus 200 feet. We could not put enough fuel in the car and it ran the fastest it has ever ran. When the Density Altitude changes to 3000 ft we see a big slow down. The same thing is going to happen with a diesel motor and pushing the air in front of it. We compute Density Altitude from barometric pressure which consists of the actual altitude where you are and the barometer reading, the humidity and the temperature. The lower the density altitude the thicker the air is and the more fuel you use to push that air.
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Old 05-14-2010, 06:26 PM   #19
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Thanks Mike. Interesting stuff. I remember density altitude from my days as a private pilot in a previous life. If you're trying to fly out of Lake Tahoe on an August afternoon... it can kill you!
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Old 05-14-2010, 07:38 PM   #20
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Yep, we used to say "the air has no lift" (lol)
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Old 05-14-2010, 08:20 PM   #21
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Does anyone have the power module from Brazel's RV performance. And did it help?
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Old 05-14-2010, 08:39 PM   #22
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I frequently see that "Well - it will do lots better after it gets broken in" bit - but I suspect that is mostly just something to salve our bruised expectations regarding MPG...

Sure, maybe SOME minor improvement as a few miles pile on - but anything REALLY significant - all things being equal, same driving style and terrain - not very likely!

If any here have actual experience after careful tests and detailed monitoring, I'd sure like to read about it...
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Old 05-14-2010, 11:04 PM   #23
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Your biggest problem with MPG is pushing a square box down the road. It is just not aerodynamic. The rear gear ratio is selected to give you the best all around performance in accelaration climbing hills and pushing that box against the air. I would not change the rear gear ratio. If you change it to less gear you can get below the power curve and the MPG will drop. The other thing is that your MH weight, transmission gear ratios, converter slip percentages, tire diameter are slected to match that rear gear ratio. Your will upset that design if you change the gear ratio.

Try reading this and see if it helps you increase your MPH. It is a real eye opener. Cummins also put one out and it says the same thing.
https://ohe.cat.com/cda/files/287140/7/LEGT5364.pdf
WOW what a great read! Thanks

on our coach 66-67 is the most efficient for us in terms of time at the wheel, distance covering, etc

the cummins turns right at 1800 - 1850 at 66-67
mpg is 7.5 to 8.0, wind and road surface is my biggest fuel killer
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Old 05-14-2010, 11:13 PM   #24
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Cummings ISB 340L and I have had as low as 7.8 with the wind square against the nose, and 11.2. The 7.8 is not typical. My typical MPG at 62-64 MPH is 8.9. When I Drop it down to 55 I have attained 11.2 mpg. On this trip out I was driving west with head and side winds. I varied from 8.9, 9.5, and 10.2. At the 10.2 MPG I did not reset and continued on at 62 MPH until I got to Calif. and reduced to 55 mph. From San Diego to Lompoc, CA, I am sitting at 9.5 mpg. The majority of that was on cruse control.
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Old 05-14-2010, 11:31 PM   #25
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I always drive on cruise control do you guys think that being on cruise Burns more fuel
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Old 05-15-2010, 11:09 AM   #26
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I always drive on cruise control do you guys think that being on cruise Burns more fuel
Perhaps not too much in purely flat terrain - but CAN suck lots of extra fuel in rolling and mountain driving, as the speed control adds LOTS of extra fuel trying to keep road speed up to it's set level...
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Old 05-15-2010, 05:31 PM   #27
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If you read that CAT performance guide for MPG it talks a little about going up and down steep hills. It indicates that cruise control can hurt mpg on steep grades because it is going to try and keep you at the speed you set rather than slow down some on the climb. It also talks about letting it have free reins going down a hill so it builds up momentum going up the next hill (within safe limits). If you are flat and level then cruise control is the answer. I broke mine once and had to drive without it. Wow was that tiring. I will gladly sacrifice a little mpg for cruise control.
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Old 05-15-2010, 05:45 PM   #28
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With our 2003 Cat 350 which I usually drive at 62 I have averaged a consistant 7.6 mpg for over 50K. I drive it hard in the mountains which is probably at least 50% of my driving. I think that is consistent with what I have read in the past from other Cat owners
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