davelinde

I know this topic has been done... but I'm just trying to make sure I understand correctly. I did some quickie searches but missed any definitive archived threads.

When towing, must I use the tow/haul mode?
I'm at near 18,000# gross towing a 5ver just over 10,000# if that matters.

The manual says "use tow/haul mode when towing". Conventional wisdom I've read is:

a) Just use tow/haul mode because the manual says so

b) Only use tow/haul if the trans starts hunting (eg up a hill)

c) Use tow/haul to get up to highway speeds, then switch out as long as the engine doesn't lug

After some experimenting I lean towards options b/c. I can hold OD (eg no hunting) on pretty steep grades as long as I start the hill going fast enough. On level ground, even down to 1600 rpm or so, all seems well. Tranny temp seems lower in OD, though EGT's seem to run a little higher.

If the trans temp is low and the trans isn't hunting... what could be the possible harm of using OD to tow heavy?

kayjh

If the transmission "hunts" in and out of OD, then use the tow/haul to lock out OD. One other thing to watch is the accelerator pedal position. Even if the transmission isn't continually kicking down, if I find the pedal must be in the bottom 1/3 of its travel to maintain speed in OD, I slow down a bit, take it out of OD (tow/haul) and drive at a slower speed to keep the revs down. I tow a 25.5' gooseneck horse trailer. Empty the trailer is about 4500#. I was able to pull it in OD at 70 mp/h into a 40 mp/h headwind in OD, except on inclines, where it would kick down. Without the headwind, or on the flat (with a headwind) it was fine in OD. Hope this helps.

Dodgezilla

If this tow/haul mode is anything like the one in my 99 Chevy Silverado, then you will also get firmer shifts which is a big help getting started, especially if your pulling 18000lb.

kayjh

It isn't and you don't.

davelinde

it isn't: going to cause harm?
and I don't: need to lock out OD?

or
it isn't: a topic that's been discussed?
and I don't: understand it correctly?

I normally like succint answers but I'm having trouble matching them to the questions.

rharveysr

Put a transmission temp gauge in and also watch the fluid temp. If the transmission is working hard in OD..you will see it on the gauge.

Rick

Srigs

Or diesel cummins have the low end grunt that you don't need to lock out unless your pulling very heavy 8k plus and only up to @60 then drop her in OD.

I have 120k trouble free miles pulling in OD 8k lbs.

kayjh

Sorry, I've been out of town. I was referring to Dodgezilla who wrote: "if it is like the transmission in my 99' Chev..."

To clear up my meaning:

"It isn't" - means that the dodge tow/haul button isn't like the Chev trans if that trans changes shift points. From 2003 to 2004, Dodge changed the label on the shift lever from "OD Off" to "Tow/Haul". Nothing else changed.

"you don't" - get firmer shifts.

As for transmission temp guages, I guess it depends on what you are towing. I don't tow 10,000# up inclines, but based on what I do tow (7,000#), on the flat or up moderate inclines (I didn't get out and measure the percentage incline), you will probably be OK in OD. As in my earlier post, in my experience, if you watch the pedal position (accelerator), I think you will know when the transmission needs to come out of OD. If you do get a trans guage, you will have to find someone at DC who will tell you what the operating range is for the trans and at what temperature you should operate it at to avoid damage. Good luck with that one. They can't even advise on the correct way to get rid of a front end pull or the dreaded vibration found on some vehicles!

davelinde

kayjh - thanks for clarifying...

I've got a trans temp gauge. I never see high temps on the highway towing in OD or without OD. The high temps I see are in stop/go traffic, starting up hills and backing up. On the highway I'm seeing 180ish on my x-monitor which uses the stock temp sender (don't ask me where that is... the pan I think). The other day I saw 240 when it took me three tries to get backed into my driveway. I don't think tow/haul mode matters in reverse...

DPG

Running in reverse, of course, there is no lock-up. Therefore the temps climb pretty quick. But we usually don't spend much time in reverse, or go very fast, so there's usually no threat to the tranny from that. The 180* while crusing is pretty normal when towing, and well within safe limits. If you would like a chart on trans. temps, PM me.

DeWain

MnTom

Dave, I have towed quite a bit in O/D. I have found that :
1. The tranny temp runs lower in O/D
2. The pyrometer runs lower in O/D while cruising
3. The boost gauge runs lower while cruising
4. My foot doesn't get as tired pushing on the throttle trying to maintain speed
5. I get about 14 mpg while pulling two trailers at 60-62 mph
I don't allow the tranny to hunt either.
Tom

stevenknapp

From 2003 to 2004, Dodge changed the label on the shift lever from "OD Off" to "Tow/Haul". Nothing else changed.

I thought I read something where it locks up the T/C in 2nd and 3rd in tow/haul? Or did they always do that?

davelinde

I'd sure like to know more about the difference between tow/haul and no tow/haul. Just got back from a quick weekend trip. I think the 5ver is another 1/2 ton or so heavier now that it's all equipped. It's also another 25 degrees warmer outside.

In stop/go highway the trans temp began to hit 220 peaks, it was typically 200-210. I didn't see it drop back to 180-190 until I found some open highway and began to cruise at 65ish in OD. As best I could tell, tow/haul just kept me out of OD and didn't help a bit with trans temp as I went from 0 to 40 and 0 to 40 in Jersey shore traffic... I played with it on and off.

kayjh

My understanding is that locking out overdrive will firstly (and foremostly) give you the mechanical advantage over your load to keep it moving. Taken to the limit of your truck's towing capacity, there is a point at which you don't have enough torque to keep you load moving (uphill for example). Locking out OD allows you to keep going.

With respect to temperatures, trans temperature has to drop when you are cruising on the open highway as compared to stop and go traffic due to increased air flow.

I'm not sure that using the tow/haul to control trans temp is really what it is all about. I think that trans temp is bound to go up in situations where you would need to lock OD out (i.e. heavier loading), so expecting the lockout to reduce trans temperature under these circumstances just might not be reasonable.

bluebull

Without reading all the previous posts I will say this. Any time the transmission is in lockup, be it OD or third the transmission will be at it's peek for cooling because most of the transmission fluid is being directed to the heat exchanger and the on to the cooler in front of the radiator. In fluid coupleing (not locked up) alot of the fluid is just droped back into the pan without going to the coolers.

The best thing to do if you can not get out on the highway at cruiseing speeds is to leave the transmission out of OD, this will allow the TC to lockup at approxamitly 35 MPH, it will lock at slower speeds if you are not stepping on the throttle. I have experience lockup as low as 26 MPH in third with keeping a constant speed.