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01-26-2010, 07:01 AM
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#21
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Family Vacation Member
Join Date: Jan 2009
Location:
Posts: 135
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One thing that T/H will do around town (or on flat areas) is tend to shift down too quickly. I tend to coast to eliminate start/stops and T/H mode makes that impossible since as soon as I let go of the gas it starts to downshift.
One area T/H excels in is communicating with the cruise control. I find the two of them will work well together to handle the ups/downs and keep the speed in check. Makes it almost too easy to drive mountain roads.
__________________
-Grant
2008.5ish Kingston KF30SB
2008 Chevy 3500 dually
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01-26-2010, 07:03 AM
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#22
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Full Time Camper
Join Date: Jul 2009
Location: Texas
Posts: 780
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What I was thinking is that the tranny is holding the revs up so therefore it has to be burning more fuel? It would stand to reason that mileage is better say at 1,600 RPM vs 2,200 RPM?
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Art and Karen
2013 Itasca Sunstar 35F, 2013 Ford C Max toad.
170 nights in 2013
132 in 2014
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01-26-2010, 07:07 AM
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#23
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Family Vacation Member
Join Date: Jan 2009
Location:
Posts: 135
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Quote:
Originally Posted by artgpo
What I was thinking is that the tranny is holding the revs up so therefore it has to be burning more fuel? It would stand to reason that mileage is better say at 1,600 RPM vs 2,200 RPM?
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In normal operation (e.g. on a highway) I don't see that. But the T/H does react to situations (e.g. foot off the gas) and then rev the engine as it trys to slow the beast down. The only place I can see it using more gas is in town or stop/go as it will tend to over react to those situations.
__________________
-Grant
2008.5ish Kingston KF30SB
2008 Chevy 3500 dually
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01-26-2010, 09:18 AM
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#24
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Weekend Camper
Join Date: Aug 2009
Location: Calgary, AB
Posts: 63
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I think that the comments relating to better mileage with the Tow/Haul mode dis-engaged are related to older style automatic transmissions where the T/H mode is actually an overdrive lockout. In this case you would have higher RPM's and lower fuel economy when driving with the overdrive lockout engaged.
I will generally drive in the city and on hills with the overdrive locked out but re-engage it on the flats for fuel economy.
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2009 CF32BL
Bumper hitch for triple tow
2011 F350 6.7L SRW Lariat
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01-27-2010, 12:14 AM
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#25
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Full Time Camper
Join Date: Apr 2006
Location: Ontario
Posts: 508
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Quote:
Originally Posted by artgpo
What I was thinking is that the tranny is holding the revs up so therefore it has to be burning more fuel? It would stand to reason that mileage is better say at 1,600 RPM vs 2,200 RPM?
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I don't think that it makes that much difference. Your Dmax with a 6spd Allison is doing about 60MPH at 1600RPM, which is about 5MPH above 5th to 6th shift point in T/H. Assuming you've got the Cruise on and you're tooling along at 60MPH,on the level, it'snot an issue, but should you start upgrade, thecomputer will try to hold that speed by pouring more fuel into the engine. This will do give you more turbo-boost, but it'll also produce more engine heat. You'll sure know it, if your clutch fan kicks in. At some point the engine is going to get hotor can't maintain the speed and the computer will downshift. Yes, the engine will speed up, but your fuel consumption will stay about the same because it's being more efficiently utilized and your engine will get more cooling.
__________________
Cheers
Helen & George VE3INB and Max (Bichon Frise)
2006 Silverado 2500HD D/A,
2006 Cruiser CF30SK
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01-27-2010, 01:31 PM
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#26
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Weekend Camper
Join Date: Nov 2006
Location:
Posts: 16
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Always on if I remember.
In the flats, my Allison trans runs about 30-40 degrees cooler with t/h engaged. When towing in the flats I see 180-190 degrees with it on... 210-220 degrees with it off. Sometimes I forget to re-engaget/h after a stop and the trans temp will start to climb until I press the button.
When climbing the trans will heat up to 210-220 degrees even with the t/h engaged. I suspect that if I tried to climb a mountain fully loaded without t/hengaged my transjust mightoverheat. I hope not to find out the answer.Edited by: TF36DSMatt
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01-28-2010, 11:34 AM
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#27
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New Camper
Join Date: Jan 2009
Location: Alberta & Texas
Posts: 3
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I tow in TH mode 95% of the time. The only time I turn it off is if it's flat or down hill, and no head or side wind. When I first started I tried may ways to increase mileage and monitored if very closely. I was unable to confirm any measurable difference in mileage.......in fact if anything my particular unit showed slightly ( .48 mpg) better in the TH mode in similar conditions. I think it keeps my revs up slightly and with a gas unit, that means more torque, and with my 4.10 gears....... 60MPH keeps it at 2000 RPM. When it hits a hill it shifts to 2500 RPM and if it is steeper it goes to 3100 RPM and it holds at 60 MPH.
My freinds diesel holds steady around 2000 RPM but, diesels get their max torque in that range and most gas engine max torque is around 4000 RPM range, and torque is what moves the load.
I think the diesels would potentially run better without TH than gas. However it is there for a reason and engine and trans cooling under load, may be valid points, as do the shift point changes.
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01-28-2010, 12:07 PM
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#28
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Full Time Camper
Join Date: Apr 2006
Location: Ontario
Posts: 508
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The Allison tranny on the Silverado/GMC gives you the best of two worlds. First, it allows you to use it in non T/H mode to operate like a car tranny, with quick smooth shifts and secondly in T/H, it gives you the operation of a commercial tranny, with wider shift points and firm shifts.
__________________
Cheers
Helen & George VE3INB and Max (Bichon Frise)
2006 Silverado 2500HD D/A,
2006 Cruiser CF30SK
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01-30-2010, 08:02 AM
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#29
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Family Vacation Member
Join Date: Jan 2009
Posts: 144
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My previous experience with Dodge and Chevy tow haul was that it locked the vehicle out of overdrive which would create higher revs. My 04 F350 and 08 F350 still allows the unit to run in overdrive where practical. Therefore, I use it nearly all the time and have towed the 36' fifth wheel all over the US including Alaska and Canada. The 04 did some drastic downshifts in mountains but the 08 is not quite as drastic on that. Happy medium would be nice!
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01-30-2010, 01:05 PM
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#30
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Seasonal Camper
Join Date: Jul 2009
Location: Idaho
Posts: 393
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Quote:
Originally Posted by carl
My previous experience with Dodge and Chevy tow haul was that it locked the vehicle out of overdrive which would create higher revs. My 04 F350 and 08 F350 still allows the unit to run in overdrive where practical. Therefore, I use it nearly all the time and have towed the 36' fifth wheel all over the US including Alaska and Canada. The 04 did some drastic downshifts in mountains but the 08 is not quite as drastic on that. Happy medium would be nice!
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The Allison tranny does not lock out overdrive!
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