F.L.U.F.
Cedar Rapids Iowa
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Joined: 09/09/2006
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My personal rule is not to start or read posts about the high price of fuel but this is a little different.
During a recent trip to Elkhart IN I decided to check the mileage of my 2000 HR with Freightliner chassis, Cat 3126, and Allison 6 speed trans.
Here's what I did... I drove a steady 60 mph across Eastern Iowa all of Illinois and half of Indiana. I was very diligent to keep the speed at 60 all the time over there and back. When I got home and filled up I was very disappointed in the 7.2 mpg I got on the trip.
I mentioned the trip to my BIL who has the exact same rig as mine with an Itasca house on it. He told me his coach will not shift into 6th speed until it hits 63 mph until then it stays in 5th. and the RPM's will be around 1800-1900 in 5th they drop to 1650-1700 in 6th.
Well I just couldn't let that info set and ferment in my brain so I took the coach for a little 360 mile trip today. Needless to say I was very surprised at the outcome..... I never let the MH go below 65 mph for the whole trip. At 65mph the fuel mileage jumped to an amazing 8.8. My RPMs did drop to 1650 and to confirm it was in 6th gear all the time I shifted it into 5th manually a couple times to make sure.
Because the shift indicator shows 6th gear all the time I just assumed it really was in 6th gear but that is not necessarily true with my Allison 6 speed trans.
Anyone ever try this test? or discover the same result as I did?
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BlackSilver
East of Heaven, North of Hell
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I have a six-speed Allison, but in a 1-ton pickup. It grabs 6th gear (on level ground) at about 60MPH (about 1500RPM), and the mileage is SIGNIFICANTLY better than at 59MPH in 5th gear!
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mavapa
Rome, Ga, USA
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Very interesting result. I wish the indicator showed the actual gear.
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gm seller
holland ny
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ditto you really have to watch the rpms to see it go into 6th gear
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Dog Trainer
Richmond Mi.
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I noticed the same thing with mine. It does not shift into 6th untill over 63 but will stay there down to about 60. My mileage is better when in 6yh gear. so 55 for me is no better or a little worse. I have an older 93 allison 3060 and my touch pad shows gear selected on one side and which gear you are in on the other so I know at all times which gear I am in. I wonder why they would have changed that.
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spitfirepete
Great Outdoors RV resort
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If you are not sure what gear you are in use touchpad to select 5 and see if it downshifts...then go back to 6
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awjoker
Ohio
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Joined: 09/22/2007
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For optimal fuel economy (on any vehicle) it is better to observe the tachometer than the speedometer. Taxing the engine is what burns the fuel, not driving at a particular speed. Keep the tach as low as practically possible.
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apr67
Tallahassee, Florida
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Joined: 02/14/2007
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awjoker wrote:For optimal fuel economy (on any vehicle) it is better to observe the tachometer than the speedometer. Taxing the engine is what burns the fuel, not driving at a particular speed. Keep the tach as low as practically possible.
The best thing to watch would be the fuel flow meter. Not standard issue on cars as of today, but I doubt it will be long. Boats with largish engines usually have flow meters.
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F.L.U.F.
Cedar Rapids Iowa
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I would never have guessed the indicator shows 6th gear when it may still be in 5th. Now that I know I can keep an eye on it and start getting better mileage.
Kind of makes me feel dumb that after all these years I didn't know. After 47,000 Plus miles I would have figured it out.
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MartyAndPeg
Jacksonville, FL 32204
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We have a device called the MIS (Medallion Instrumentation System) which is pretty common on Freightliner XC chassis, and keep it set to the E-Info screen, which shows speed, RPM and current gear.
I'm not sure what speed I have to be running before it kicks up to 6th gear, but I am sure it is not 63. We will leave Raleigh, NC on Wednesday (continuing our northern trek) and will keep an eye on when the shift occurs (and the raod conditions).
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