Go Back   iRV2 Forums > MOTORHOME FORUMS > Class A Motorhome Discussions
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
Thread Tools Search this Thread Display Modes
Old 10-08-2007, 05:16 PM   #15
Senior Member
Join Date: Sep 2004
Posts: 713
This is something which might help, sent form a friend who monitors a Caterpillar forum. I doubt the Cummins will change the way the Allison tranny works:

There are TWO TOTALLY DIFFERENT "LET THE TRANSMISSION CHOOSE THE CORRECT GEAR" MODES/PROGRAMS in the Allison ECU which is the "electronic brain" controlling shifting and other functions.
In ECONOMY MODE, the transmission will not downshift even at WOT
(Wide Open Throttle) until the engine pulls down to peak torque RPM in some application and 200 RPM lower that "regular mode" in others.
In REGULAR MODE, the transmission WILL downshift much earlier (to maintain higher engine RPM).
ONLY at higher throttle positions is there any difference, so on flat ground you will NOT notice any difference (except accelerating from a stop IF you are at or close to wide open throttle).
It can make a BIG difference in rolling hills. If you are in rolling hills and regular mode (particularly with the cruise control on), it is common for the transmission to shift down to 5th on the uphill and back to 6th on the downhill. Repeat this process hundreds of times. In economy mode, you will stay in 6th gear unless the hill is so steep or so long that the engine can not pull it without dropping below peak torque RPM. If you can pull a hill in a higher gear (lower engine RPM) AND the engine does not overheat, THAT IS WHAT CATERPILLAR RECOMMENDATIONS FOR THE MOST ECONOMICAL WAY TO CLIMB A HILL with a modern turbo, after-cooled diesel engine.
If you know you will need a lower gear because of the steepness of the grade and/or are engine temperature is rising higher than thermostatically controlled temperature, if driving in economy mode, use the down arrow to drop a gear (this is what I do) or switch out of economy mode. Be sure to switch back into economy mode when past the steep section, or agree to pump extra fuel in the tank.
IF your engine begins to overheat, your HP/weight ratio is low OR if it irritates you to loose a few mph on a hill in the name of saving fuel, in the hills, by all means drive in regular mode.
It confuses me to hear people advocate driving in economy mode only on flat ground, as there is not 1% difference in shift RPM's between regular and economy mode on flat ground, excepting accelerating from a stop if you use WOT.
Every time you start the coach, the transmission is in regular mode. This is the default setting. IF you push the mode button, it goes to "economy mode" AND the light illuminates.
There is no "absolute" on how much difference in fuel economy driving in economy mode will have. On flat ground where you will be in 6th gear irrespective of what mode you are in, there will be ZERO difference. The MOST difference in mileage will be in rolling hills, where in regular mode, particularly if on cruise control you will start up a hill in 6th gear, go to WOT in 6th gear, downshift of 5th gear still at WOT (WHERE IT IS USING A LOT MORE FUEL). After the hill is crested, the transmission will up-shift to 6th, then likely coast a little in 6th gear (unless you are driving with the exhaust brake on-- if you are it then applies the exhaust brake AND downshifts TOWARD the pre-select gear which is generally either 2nd or 4th).And so on 6-5-6-5-6-5-6-5.......
A modern turbo inter-cooled diesel is much more efficient at low RPM high throttle settings. This is NOT my opinion. It is stated in just those words in the Cat Owner's Manual.
Note: In either mode, you are free (and welcome) to use the up and down arrows to PRO-ACTIVELY choose the correct gear. You can not screw anything up-- even if you down-arrow to 1st gear at 70mph, the transmission understands that you meant "please downshift to the next lower gear as soon as the engine RPM will not exceed the pre-set amount. Then downshift again when safe....."
By the same token, you can shift between regular and economy mode as often as you want with the transmission in any gear when you make the change.
OPINION: I drive in economy mode 99% of the time, including in REAL mountains, but use the up and down arrows to choose the proper gear. I use regular mode ONLY when I am willing to say, "I am willing to throw a lot of fuel away to gain a little performance." When passing on 2 lane roads, THIS IS the case.

cwg is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 10-09-2007, 03:05 PM   #16
Senior Member
Alpine Owners Club
Join Date: Mar 2006
Location: Oregon
Posts: 348
Way Back in the old days (60's) I spent some time as a livestock hauler and 318 GMC and 300 Cummins was the big deal. I was taught when pulling a hill, if you could not accelerate even ever so slowly, you were in the wrong gear especially at the lower end of the rpm range creating enough heat to burn piston heads. Maybe that is ancient history but my 2 cents on the subject.
I had not figured out the mode button on our newly aquired 36. Thanks cwg for the info

05 Alpine 36MDDS, 09 Subaru Forester, no animals.
two sailors is offline   Reply With Quote

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Stimulating the Economy fshrmndave New Rig Show-Off! 2 01-10-2009 06:04 PM
GOOOOOOOOOOOOOD ECONOMY??????? cannon man Workhorse and Chevrolet Chassis Motorhome Forum 14 09-21-2008 05:24 PM
A/C and Fuel Economy LouisB National RV Owner's Forum 8 08-22-2008 07:27 AM
What is the "Economy" setting? Allison Transmission Forum 15 12-31-1969 07:00 PM
A/C and Fuel Economy MH-General Discussions & Problems 8 12-31-1969 07:00 PM

» Virginia Campgrounds

Reviews provided by

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 10:08 PM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.