Tow/haul or not tow/haul that is the question

[Marcross1009]

So I've been towing with my 21 3500 srw HO Cummins to tow a 40ft travel trailer (approx 11k) and noticed a lot of the time I am running 60mph or so on fairly flat land and with tow haul on it will not kick into 6th gear, if I accelerate to 65+ and then slow down it will shift and not downshift to 5th unless I slow below about 55(ish). I did try turning tow/haul off while cruising 60mph and it immediately shifted to 6th. Other than the exhaust braking, which is great btw, if I'm just cruising and not pulling hills or anything will it hurt the transmission to kick off tow haul so it will kick into 6th? I've checked and normal towing with tow haul the trans temperature sits between 150-170. I wasn't sure if it would heat up not in tow haul, which is why I haven't experimented more than turning it off once. I would like to get the extra mpgs but not at the cost of hurting the transmission. So will it hurt the transmission to tow not in tow/haul mode?

 

[elephantrider]

how many extra mpg do you think you'll get? answer is, hardly anything with a 40ft rv behind ya. keep t/h engaged and let it do its thing.

 

[sanda]

When towing on the flats I often turn off tow haul. If the truck starts hunting gears just put it back into t/h.

 

[H3LZSN1P3R]

Heres my thought on it even though the aisin is a tough trans. Is the little bit of better fuel millage (maybe 1-2MPG) worth the cost of a trans if it did fail? Its unlikely to fail if not hunting for gears but with the truck sticking in 5th its giving you a better RPM range to keep the engine happy and the trans line pressure happy

 

[AH64ID]

I will occasionally kick it out of TH at 60-65 if I am on a downhill or have a big tail wind, but it's not common.

The trans likely doesn't care, but the EGTs and ECT rise on the truck from lower flow. Not to a bad point, but higher than 5th.

The lie-o-meter doesn't really show any appreciable difference with a load behind the truck as the truck still has to make the same hp and the rpms aren't that different.

 

[Bombaman]

Only use Tow-Haul if its shifting constantly (inline with Owners Manual), so really only in hilly terrain, otherwise just leave it.

 

[Will_T]

Interesting conversation. With my smaller TT, (probably 8,000 lbs. max), I have been using Tow-Haul and locking out 6th gear. I am generally about 65 mph on the open road and it keeps the RPMs up in what seems a better spot than 6th gear can drop them to. I notice no hunting at all and on most inclines, it does not even need to downshift. On steep uphill when I sometimes get into the right lane with slower traffic, I will even lock out 5th gear. I did not notice an appreciable difference in mpg when I started doing this. But in any case if I am towing the TT, I use Tow-Haul. There have been a couple of stretches where I forgot to put it back on after a stop and I did not notice anything different. So with a TT the size of ours, I am not sure it really matters if you use Tow-Haul or not?

 

[AH64ID]

Interesting conversation. With my smaller TT, (probably 8,000 lbs. max), I have been using Tow-Haul and locking out 6th gear. I am generally about 65 mph on the open road and it keeps the RPMs up in what seems a better spot than 6th gear can drop them to. I notice no hunting at all and on most inclines, it does not even need to downshift. On steep uphill when I sometimes get into the right lane with slower traffic, I will even lock out 5th gear. I did not notice an appreciable difference in mpg when I started doing this. But in any case if I am towing the TT, I use Tow-Haul. There have been a couple of stretches where I forgot to put it back on after a stop and I did not notice anything different. So with a TT the size of ours, I am not sure it really matters if you use Tow-Haul or not?

I have found that a trailer below 4K lbs does not really warrant TH, but above that I like the difference.

If I forget it at a stop it’s hit and miss as to how quick I notice it, but usually it’s when it drops into 6th way too early.

It would be nice if TH and EB were remembered positions.

 

[jsalbre]

With the Hemi and 4.10s pulling a 7k trailer I’ve been unable to notice a difference with TH on or off, even in the mountains, other than it disabling cylinder deactivation.

I noted the same thing on my 2020 pulling a 9k trailer.

 

[H3LZSN1P3R]

I have found that a trailer below 4K lbs does not really warrant TH, but above that I like the difference.

If I forget it at a stop it’s hit and miss as to how quick I notice it, but usually it’s when it drops into 6th way too early.

It would be nice if TH and EB were remembered positions.

They are remembered with tuning! Its silly they are not setup with a memory

 

[AH64ID]

They are remembered with tuning! Its silly they are not setup with a memory

The C&C programming remembers the EB position, and my truck will occasionally remember it... It should ALWAYS remember it.

 

[H3LZSN1P3R]

The C&C programming remembers the EB position, and my truck will occasionally remember it... It should ALWAYS remember it.

It should your right its a stupid oversight i think

 

[Ronstar]

Newbie question….. I have an 01 with the 5sp manual. I generally leave it in 4th around 60 mph which results in +\- 2200 rpm. Unless steep grade it stays right at 55-65 depending on the road/curves etc. Reading all the above no one mentions rpm so what optimum should I be looking at with my 23????
26’ TT at 7500 lbs

 

[jsalbre]

Newbie question….. I have an 01 with the 5sp manual. I generally leave it in 4th around 60 mph which results in +\- 2200 rpm. Unless steep grade it stays right at 55-65 depending on the road/curves etc. Reading all the above no one mentions rpm so what optimum should I be looking at with my 23????
26’ TT at 7500 lbs

If your 23 is a Hemi, then I’d say the 8 speed does an excellent job picking gears, so I wouldn’t worry about it. I can’t speak for the 6 speeds on the diesels.

 

[jebruns]

Interesting conversation. With my smaller TT, (probably 8,000 lbs. max), I have been using Tow-Haul and locking out 6th gear. I am generally about 65 mph on the open road and it keeps the RPMs up in what seems a better spot than 6th gear can drop them to. I notice no hunting at all and on most inclines, it does not even need to downshift. On steep uphill when I sometimes get into the right lane with slower traffic, I will even lock out 5th gear. I did not notice an appreciable difference in mpg when I started doing this. But in any case if I am towing the TT, I use Tow-Haul. There have been a couple of stretches where I forgot to put it back on after a stop and I did not notice anything different. So with a TT the size of ours, I am not sure it really matters if you use Tow-Haul or not?

Easiest way to tell is try towing it w/o tow/haul on and tranny not locked out of 6th. If it's shifting down a lot, use tow/haul. Otherwise, don't bother.

 

[H3LZSN1P3R]

Really the best reason to use tow haul is for the better exhaust braking for the diesels not so much the gear selection

 

[AH64ID]

Newbie question….. I have an 01 with the 5sp manual. I generally leave it in 4th around 60 mph which results in +\- 2200 rpm. Unless steep grade it stays right at 55-65 depending on the road/curves etc. Reading all the above no one mentions rpm so what optimum should I be looking at with my 23????
26’ TT at 7500 lbs

I’m assuming diesel on both, so if not sorry.

Whatever gear it puts itself in, they won’t hurt themselves. At 7500lbs I would personally use TH, which means you won’t be in 6th at 60.

The 6.7 is a very different beast than the VP 5.9. Between the added displacement, a variable geometry turbo, and HPCR the 6.7 is much better at low rpms. With an automatic transmission you can’t lug the 6.7, it won’t let you. The 2200 sweet spot on a VP 5.9 might be closer to 1800 on a 6.7. The 6.7 has adequate boost and programming to pull hard from ~1400-redline, and it will select the best gear to do that under most circumstances.

So use TH when you’re heavy, and let it’s do it’s think. You will rarely have to use the ERS to lock out gears, and when you do it’s usually due to rolling hills or long steep slow hills.

 

[darrellr]

It should your right its a stupid oversight i think

I wonder if it is an environmental decision. Both EB and TH mode can negatively impact fuel economy. I bet someone decided the best option is the most fuel economical choice which is to turn both off just in case people forget to do it themselves.

 

[H3LZSN1P3R]

I wonder if it is an environmental decision. Both EB and TH mode can negatively impact fuel economy. I bet someone decided the best option is the most fuel economical choice which is to turn both off just in case people forget to do it themselves.

Doubtful but who knows how those peoples mind work, i still think its a CYA for the EB in the winter incase its extremely icy but its just a speculation

 

[AH64ID]

Doubtful but who knows how those peoples mind work, i still think its a CYA for the EB in the winter incase its extremely icy but its just a speculation

That’s my thought as well.