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Old 03-26-2010, 09:16 PM   #11
Bill
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John -

Your owner's manual ought to cover this. Find it online if you don't have a copy, but it is probably in the glove compartment.

For my Ford, the owner's manual says to turn it off to prevent excessive shifting (also known as hunting). This will prevent the transmission from shifting repeatedly amongst 6th, 5th, and 4th gear as I go up and down minor grades, by locking out 5th and 6th gear. It is the act of shifting that is hardest on a transmission, especially if it is done under load.

So again in my Ford, I leave it alone if I am on the flats and moving along nicely (65 mph or so). The tranny locks up in 6th gear, and stays there. But if I have to slow down, or if the terrain gets hilly (not mountains, or even steep hills - just a bit hilly), I will notice that the tranny starts hunting for the right gear, and I hit the button to prevent it.

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Old 03-26-2010, 09:24 PM   #12
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Previously I had a ford explorer with the V6 210 hp. With my 2720sl, I always had the over drive off on any type of uphill grade. However, in completely flat areas such as the prairies of midwest canada it rolls along so easily that I usually left it in Overdrive to save gas. I also did this down long gentle grades where you do not need the engine braking.
If it is under very little stress you might as well save some gas, but I imagine this depends on the towing power of your tow vehicle. I think the ford explorer has about 250 ft-lbs of torque and it towed easily in Od in those situations.
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Old 03-27-2010, 06:31 AM   #13
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I turn off the OD if it starts shifting in and out a lot (hilly country). On flat land I leave it in to help on mileage.

(edit) should have read the 2nd page. Basically I'm echoing Bill's response.
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Old 03-27-2010, 09:59 AM   #14
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Default FWIW - mileage comment

The first year I had my TM (2008) I towed primarily with the OD on. Thinking, as others have said, that I would get better mileage on flatland (although not much of that here) and it would kick to a lower gear naturally when climbing. Last season (2009 summer) I decided to tow almost exclusively with OD off and see what happened.

1. I noticed that I was a lot more comfortable towing - didn't seem to downshift as much and I had a significantly better experience pulling over passes (i.e. Berthod and Monarch for those familiar with Colorado).
2. The biggest surprise was that I didn't seem to have any difference in mpg. I would get consistently 11-12 in OD and 11-12 without.

Granted, my numbers are not based on scientific or even strong empirical evidence. Just my observation of mpg when I reset my trip computer.
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Old 03-27-2010, 11:31 AM   #15
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Quote:
Originally Posted by Al-n-Sue View Post
The first year I had my TM (2008) I towed primarily with the OD on. Thinking, as others have said, that I would get better mileage on flatland (although not much of that here) and it would kick to a lower gear naturally when climbing. Last season (2009 summer) I decided to tow almost exclusively with OD off and see what happened.

1. I noticed that I was a lot more comfortable towing - didn't seem to downshift as much and I had a significantly better experience pulling over passes (i.e. Berthod and Monarch for those familiar with Colorado).
2. The biggest surprise was that I didn't seem to have any difference in mpg. I would get consistently 11-12 in OD and 11-12 without.

Granted, my numbers are not based on scientific or even strong empirical evidence. Just my observation of mpg when I reset my trip computer.
You are correct. Any difference would certainly be imperceivable and completely unprovable. Even if one were to drive the exact same route at the exact same speed, there are so many different variables that it would be impossible to determine which variable may or may not have made a difference in MPG.

Shifting out of OD, while towing, would show no perceivable difference in MPG and just simply not worth the added wear & tear on the vehicle.

My advice would be to use "Tow Mode" on your vehicle while towing, not doing so (under any condition) could be risky........ IMO.
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Old 03-27-2010, 12:17 PM   #16
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So if it doesn't help with mileage, wears the transmission out faster, and is unsafe, why does my truck have overdrive installed?

I guess to keep the service business rolling in to the dealer
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Old 03-27-2010, 12:48 PM   #17
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Thumbs up "Tow Mode"

John, I'll drop my 4Runner shift selector to "4th" when towing on grades (even moderate grades, less than 3%). And on big hills, my Toyota's shift points don't downshift as early as I'd like -- I basically run it as a manual, keeping it at about 300 RPM's higher than my V6 would choose.

I know that your Tundra, in comparison to my 4R, is massive overkill for a 2619. (Until you get into the mountains, which is pretty quick in COS -- or in Southwest Reno.) Since they did give you a special "tow" button, it probably does everything I do by hand -- disabling 5th and downshifting more aggressively. Unlike your button, however, I'm very comfortable with 5th on level roads and slight downgrades (those which don't need a lower gear to provide a just a bit of engine braking.)
- - - - -

For everyone, I point out a simple fact: When you're stomping the gas peddle way down to "lug" up a hill with your Trailer, you're getting worse gas mileage than revving the engine in a more favorable range. (It doesn't just wear your Drive Train components, it costs you at the pump too. They didn't program the Tranny computer with a trailer in mind-- it's optimized for gas mileage under EPA testing conditions.)

If you don't get a good power response when you push your foot down a bit more, you should probably be changing into a lower gear.
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Old 03-27-2010, 12:49 PM   #18
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Yeah, I was joking. I always get worse mileage when I take it out of OD....but then, that is when I am in the hills! Could be some relation there I guess.
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Old 03-27-2010, 12:51 PM   #19
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Quote:
Originally Posted by wbmiller3 View Post
So if it doesn't help with mileage, wears the transmission out faster, and is unsafe, why does my truck have overdrive installed?
I guess, because they imagined that their customers would not be towing trailers 100% of the time.
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Old 03-27-2010, 01:35 PM   #20
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I guess that some of this depends on one's age too.....

I used to take it out of "Tow Mode" (a button on the gear shift lever) when going down a long gradual slope. The problem is, I would often forget to switch back when I got to the bottom of the hill .

I decided that it is better to just "Set-it and foget-it".
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