That is just the nature of the 5.7l Tundra, it is generally a high revving motor when towing. Tow/haul mode only changes shift points and holds gears longer. You can put it into standard mode and limit it to only the gears you want. My boat weighs right around 4000lbs and when I would tow it with my Tundra it would downshift even on slight hills. The reason it has to downshift or "hunt" is because the power is made at higher rpms.

So the answer to your question is no, it will not hurt the truck to leave it in normal mode when hauling 5000lbs. However it's not going to change much of anything, it will still rev up and downshift.

 

If you're gonna leave that 6 speed transmission in "D" to do the thinking for ya,then use the Tow-Haul mode.I like the Sequential Shifter and how easy it is to use, so I'll pick which gear to be in for a given load and situation,we're the ones with the brains here right?I see NO point in Tow-Haul.:thumbdown:Just my opinion.

 

here in the flatlands of Florida it isn't needed as much as in mountainous areas.

Answered your own question.
With the tow package, you're already geared for towing and you will get engine breaking even when not in T/H mode. You will still have engine breaking when not towing at all, for that matter.
The tundra doesn't give a shit about 5000 lbs. you can tow that all day without needing higher shift points or T/H mode. Especially in the flatlands.
You're all good.

 

E85 I would run tow/haul + 5th gear in flat to hilly terrain
Regular fuel tow/haul button.

 

Super old post but Damn, I can't imagine the crappy mileage towing on E85...I bet it got about 4 MPG.

 

This has always been a hot subject. IMO I would use S mode and no tow/haul. But if you feel the truck is handling it fine, then it probably is. Your boat probably doesn't have the surface area that travel trailers do, so it will be easier to tow vs a similarly weighted trailer. Tow haul will also alter the throttle map. (hence the higher shift points) I personally don't like to use "D" for towing as it takes some time for the trans to re-adjust to not towing afterwards, but I am in a mountainous area, and that may have something to do with it. by using the S mode, the trans won't adapt (removes the learning part) to the trailer and when I unhook I keep my nice low shift points for fuel econ.

 

S mode question



So this may be a really silly question but I have to ask. If towing in S does tow/haul button still do it's thing or is it not active when using S mode??

 

Interesting...I'm coming from a 2012 Honda Pilot (Honda V6's are 3.5L FYI) which has 250hp and about the same torque...around 250 lb-ft. Compare that to 380hp and 400 lb-ft, and I'm surprised you are seeing the same high RPM while towing the same trailer you pulled with the Honda. But is it really the same?

My Pilot would rev high, very freely even during easy throttle, towing my 4300lb TT. Getting on the freeway, I would bounce it off red line thru 3rd gear to quickly get to speed. Had I not, well...I just dont have that type of patients! And this never phased the Honda, despite people thinking Honda's cant tow.

I've only towed 2 hours with the 5.7L since I've owned it, but engine and trans wise...I was surprised how easily the motor rev'd high with easy throttle. BUT...

....But then I turned on tow/haul mode, things changed. It did not rev as high, because it changed gears at lower RPM, UNLESS I was really on it. Throttle response changed also, were I needed less application to get the same acceleration. I believe thats just trickery with the throttle-by-wire, but I liked it.

Regardless if you can feel or notice these differences...or not, why would you not turn on tow/haul when towing? I'm not clear what possible reason there is, unless you're shifting manually, then tow/haul is not inactive anyway. It's designed into they system with a clear intent, so I intend to use it!

 

I can only speak toward towing a few Sea-Doos which touch 3K pounds. I tow that without the Tow/Haul but I did try it once. Yeah, it's not needed for 3-4K pounds. I did tow the skis up and down a pretty steep incline/decline but like someone else said here, I manually shifted.

I figure try it both ways and see what fits the bill. Buddy has an 8K trailer and uses the tow/haul mode. He mentioned it does help. I figure wet, with gear and all, he has to be about 9,500lbs. I surmise the tow/haul is for the heavier stuff.

 

I drive with the T/H on all the time, unloaded..
I like the higher shift points and engine braking

 

^^^. Me too.

 

On flat roads with open traffic, I would put it in Drive and not worry about it. You'll be fine and get much better MPG. That being said, if there is a lot of traffic, stoplights, or hills then use the T/H mode if you're pulling more than 3 to 4k lbs (IMHO). Its a benefit, you have it, so use it.
What's the benefit? The change in shift points will generally reduce the # of shifts while driving, will run truck at the same speed at higher RPMs (lower gear) than when not in T/H mode; thereby increasing the available power and torque and acceleration at any given speed in any given situation. It will also downshift LESS in slightly hilly terrain, or 'stop n go' traffic. I see the T/H mode is more for a protective benefit for the transmission than the engine. This will put less stress on the transmission (perhaps more on the engine, but the engine can likely handle whatever you're dishing out).

I'm not a mechanic but I pull a pretty heavy trailer fairly often, in both flats and hills. This has been my experience and understanding of it after several years, different trucks, and a fair amount of research on the subject.

 

I tow my Jeep on a 20' car hauler from Texas to Colorado every year and it weighs 6500-6800 and I always have towed using S5 with tow/haul on. That seems to be were it pulls the best for me and I get the best mileage 9.5-10 avg.

 

@cptzeon, When in sport mode it just limits the top gear, it will still downshift when you are stopping/slowing. The T/H
still does it's thing.

 

My father recently got rid of his 2014 Tundra Crewmax 1794 for one reason... and it was because it wouldn't hold cruise while towing his travel trailer. Any hill he came across, it would downshift to 5th, then 4th, and then once it shifted to 3rd the cruise control would reduce engine rpms to around 3000rpms and would hold it there. Annoying to say the least and is one of the most annoying, and stupid things Toyota did to the Tundra after the 2007-2008 year models. My father's previous 2008 Tundra, never had these issues... it would cut cruise control off but it wouldn't reduce rpms etc and maintain cruise at 3000rpms and 45mph.

His 2008 had 156,000 miles when he traded for the 2014 Tundra... and boy was he pissed after that first trip towing his travel trailer. I'd sure as hell hate to constantly have to monitor speed etc for 2500+ miles towing.

So is there a point where the Tow/Haul mode makes a difference, yes around town there is a benefit. But it is truely useless in the aspect that the only cruising you can do with a decent trailer behind you is on a level highway with no headwinds. I love the way the Tundras ride and drive, but if your towing any decent amount... either stick with the 2007-2008 year models or buy a different brand.

 

Oh great, he's back .....

 

All manufacturers, including Toyota specifically call out towing as a situation not suited for cruise control.

 

They absolutely do NOT.

The context these OEM comments are printed in, is cautionary. Read the heading of the page. Read the other list of cautionary statements.

We can absolutely use cruise while towing.

Speaking of cautionary...its why cruise kicks out if it has to drop to 3rd gear. This is just simple common sense. If your towing at such a speed and resistance that the truck drops to 3rd and floors it to retain set speed, you need to be in full control of your vehicle at that point.

 

Quick question while we're on the subject. Is there a certain time you're supposed to turn the tow/haul mode on? Is it ok to do it while you're driving, or are you only supposed to turn it on when you're parked?

 

It is only a program mode for the computer. Nothing mechanical is involved. I do it anytime.

 

I pull a 7,000 lb fifth wheel trailer and have done about 7,000 km towing it so far. I find the Tow/Haul works just fine except for the steeper hills. On the steep hills and in cruise it does the final shift down to put rpm at about 3,500 sits their for a few second and then gives up -- while totally dumping the cruise. You have to set the speed again. I suspect there is a maximum fuel limiter that kicks in and dumps the cruise. I have found through experience that when it makes that final shift up there is lots of power if you help it out with the gas pedal before it dumps the cruise. There is enough power to accelerate easily above your cruise speed, so it is not jamming due to lack of power. I suspect it is a lawyer designed anti-runaway Toyota control. The manual assist with the gas pedal is no big deal as you know when you are going to need it - only on steep hills. Way easier to help it out now and then with manual assistance than to drive thousands of km not using cruise.

I have never tried the standard mode for towing other than short distances when I forget. I suspect you do not hurt anything by using it. When in Tow/Haul it switches between three gears with and without lock all the time. On a level road with no wind it spends most of the time locked in 5th. It occasionally shifts to 6th, and occasionally to 4th. I have found into a strong headwind it spends most time in 4th and sucks a lot of gas - about 30% more. Sure makes the gas tank small!

 

That is just how toyota has the truck programmed, thats exactly why my father dumped his 2014 tundra because its a PITA to tow long distances without cruise while towing. This was put in place by toyota from 2009 forward.

 

I tow a 4,200 lb camper. I use the tow/haul mode and S5. I am concerned about overheating the tranny, so I monitor the tranny temp with an UltraGauge. On long hills, I will see the tranny temp start to climb and I will down shift to S4 and usually the tranny temp will drop. I don't use cruise when towing, although I can see where it would be nice on long level stretches.

 

This is why vehicle manufacturers tell you to not tow in Overdrive. When you run the transmission under load as in when towing you are lugging that transmission quite a bit causing a lot of excessive heat. So when you downshift to a lower gear you will reduce the heat in the transmission because the transmission cools the fluid by circulating it through a transmission cooler most of the time if you have a tow package. The lower RPMs will not allow the transmission to pump that fluid fast enough to keep it cool...so when you drop to a lower gear increasing the RPMs it allows the transmission to work less and push that fluid through the transmission cooler faster to help keep it cool.

Heat is what kills an automatic transmission doesn't matter what vehicle its in, overheat the transmission and its more likely to fail.

Cruise control could be used if you are on flat ground, but if you are driving through areas with a lot of hills its best to use a lower gear, and not use cruise control anyways.

 

Tow/Haul on, cruise set to 75mph, 5th gear.

Tow/Haul on, cruise set to 75mph, dropped to 4th gear

In the examples above, I allowed the truck to shift as needed while under cruise. But often enough, I would hold it in 4th to maintain the high speed and not shift, if it was shifting often. MPG's did not waiver running the same speed, same need for X amount of power, regardless of RPM.

Similar to towing the same trailer with a smaller V6 SUV, RPM's play very little role in MPG when driving a consistent line. I could run 4,000+ with the V6 all day and get the same mpg as when I allow it to upshift. I basically find the same with everything I have towed with.

Fuel delivery is very precise. These systems/engines wont dump more fuel in just because the engine is spinning faster. It will only deliver the fuel it needs to produce the power you are demanding.

Those who think keeping RPM very low while towing may actually be reducing their MPG, as you're purposely lugging the engine vs spooling up to produce the more efficient power.

There was a claim of 4th gear using 30% more fuel. Conditions and desired speed probably played a bigger MPG role than just running 4th vs 5th gear.

 

Tow/Haul on, cruise set to 75mph, 5th gear. Those who think keeping RPM very low while towing may actually be reducing their MPG, as you're purposely lugging the engine vs spooling up to produce the more efficient power..

Actually most engines do get better fuel economy when they are at lower rpm and close to lugging. The reason is that the intake manifold pressure is less negative and the engine runs more efficiently when it isn't fighting a negative pressure in the intake.

Also keep in mind that most ST trailer tires are not rated for more than 65 mph.

 

i dont understand why I cant use CC when i'm driving my kids to school, I'd like to engage it at 25mph but it wont let me.

I think i'm going to sell my tundra... its such a piece of shit.

 

Try 26mph

 

All those charts are nice, I have seen a couple before, not nearly all of them.

I don't think they apply at all to towing. Reality is, when we apply full throttle, the trans will down shift and RPM's jump. This is true of gas and diesel when towing.

And in my experience with multiple tow vehicles of different engine sizes (from manual and auto 4cy and 6cy, to V8's. Including not my own, one F-150 Ecobust and a Flex Ecobust). When a specific speed is on call vs driving for best MPG, it doesn't matter what gear is used (or held)..to a point.

For the 5.7L, it has been 4-5th. For others it was only an option to turn off OD, and drop to 4th and run that all day. For most manual trans, it was 4th and occasionally 5th. 5th gear in the manual V6 and 4 bangers, most often lugged the engine and just sucked gas with no go.

We can debate this all day long with Google, but my results over many decades always end up the same. Do what works for you. I get great MPG compared to most for the speeds I travel when towing and not towing, so I must be doing something right.

 

I don't think they apply at all to towing. Reality is, when we apply full throttle, the trans will down shift and RPM's jump. This is true of gas and diesel when towing.

And in my experience with multiple tow vehicles of different engine sizes (from manual and auto 4cy and 6cy, to V8's. Including not my own, one F-150 Ecobust and a Flex Ecobust). When a specific speed is on call vs driving for best MPG, it doesn't matter what gear is used (or held)..to a point.

The graphs apply to the engine, and certainly are accurate for towing as well as normal driving. A well designed vehicle will try to put the engine torque and rpm in the middle of the high efficiency island when in overdrive at 60 mph or perhaps a little higher. The vehicle will be designed around the EPA fuel economy test standards so the engine when in test spends as much time as possible in the high efficiency island.

When we tow, we need more HP. That means more torque and rpm. A well designed transmission program will most likely increase torque first and then rpm as required to keep it in the highest efficiency zone possible. However in general because you are going to the right on the graph, it is going to be at the lowest possible rpm that still provides enough power.

The graph for the Prius is a good example of how you maximize fuel economy with the engine/transmission combination. The red line on the graph at this link is the how the overall drivetrain is programmed.

Brake Specific Fuel Consumption (BSFC) Maps - EcoModder

First the engine rpm stays the same, and just the torque is increased, virtually straight up, because that is the shortest route to the high efficiency island. Then it starts to increase rpm to get into the middle of the high efficiency island. You will probably be at about 60 mph when in the middle. However if you want to accelerate or go faster then you will start to go to the right just like in towing. You simply need more power which at the same torque means more rpm.

My conclusion for the 5.7 Tundra and while towing is that if the wind and road grade allow the best mileage is achieved when you are in 6th gear and locked up. Second best is 5th gear and locked up. 6th gear and not locked is likely lower efficiency that 5th locked, so you want to minimize that time.

However, I have no use for trying to outguess the engine designers. I just put it in Tow/Haul and cruise. If they have done their job, and they certainly will be well aware of the brake specific fuel consumption map, the engine will be kept in the most efficient operating zone. I trust Toyota over my own judgment. After all that is what the Tow/Haul mode was designed to do.

And as for diesels they have similar maps. The big difference with a diesel is that they have very high torque at low rpm. That means they can stay at lower rpm and high torque to produce highway speed towing power. That is how they beat the gas engines for fuel economy.

 

Diesel engines are naturally more efficient based on fuel energy content, not lower RPM. Again...RPM plays a small role.

Gas/E10 = 112-116k BTU/GAL

Diesel = 128k BTU/GAL

I don't need to write a book to explain simple things.

 

I don't need to write a book to explain simple things.

I wrote a book, because you don't seem to get it.

 

@Ron AKA - What you are saying isn't wrong per-say, you're just applying terms and charts to a topic and view they don't belong.

The OP said while using T/H mode; "Shifts way beyond what RPM would seem needed w/the kind of power it has. I think it's costing a lot of extra MPG for no reason."

I chimed in to say that's not exactly true...of any vehicle I've ever towed with.

Consider our trucks make 381 hp @ 5600 rpm and 401 lb.-ft. @ 3600 rpm.

If your goal is MPG, then by all means you will want a high gear and allow the truck to slow on hills and not downshift to maintain speed.

If you want to maintain speed, with T/H on, the truck makes a greater attempt to hold the low hear, until speed drops too low...it will always downshift.

Where is our engine most efficient for power and efficiency? I cannot say. If we knew, would we all attempt to lock our speed and gear to hold this exact position? Some might...I wager most wont care. But I can tell you any car/truck that always attempts to keep RPM at its lowest, when speeds are NOT constant (stop and go, slow acceleration) will NOT achieve high MPG. Moderate acceleration to get up to speed, then holding that speed is best for general driving...but not always the case for towing.

ANYWHO. In my pics you see I'm towing at 75mph in 4th and 5th. 5th gear at this speed puts me at peak torque RPM but I'm not full throttle, seemingly still a great spot to tow. But yet a very mild grade will force a downshift beyond my control to 4th, so I would often lock in 4th. Regardless of gear, at this constant speed, MPG was not affected by RPM, which has been repeated in everything I have towed with.

This was/is my main point for the OP. Repeated. Argue whatever other details you want. I really don't care.

 

[MENTION=207145]
Where is our engine most efficient for power and efficiency? I cannot say. If we knew, would we all attempt to lock our speed and gear to hold this exact position? Some might...I wager most wont care. But I can tell you any car/truck that always attempts to keep RPM at its lowest, when speeds are NOT constant (stop and go, slow acceleration) will NOT achieve high MPG. Moderate acceleration to get up to speed, then holding that speed is best for general driving...but not always the case for towing.

The torque and rpm (1600 or so) where the truck is at when driving at 60 mph in 6th gear and not towing is probably pretty close to the optimum for engine efficiency. If it wasn't they would change it to get better results out of the EPA highway mileage test. That is not enough power to tow with so torque has to go up, and then rpm. The higher the rpm goes up the poorer the efficiency. But the overriding factor is that you need the power, so efficiency has to suffer.

 

Just for the record the torque converter does lock in 4th gear as well as 5th and 6th. I tow a 5th wheel that weights 9600 lbs when loaded with my 2011 Tundra reg cab long box (1820 lbs payload). I am legal weight wise in all regards but only by about 100 lbs on truck GVWR and 300 lbs on combined gross. My practice after many thousands of miles towing is to just use S4 and I run about 60 MPH at 2800 Rpm. Truck very happy at that speed, not laboring at all and I use cruise control unless there are substantial hills. My experience with this weight is that I gain very little by using 5th unless a good tailwind and transmission hardly ever needs to shift unless steep hills. I average about 10 MPG on US gallon. My reasoning is that there is much less strain on transmission when it is in 4th gear which is direct drive. I figure at the price of a new transmission I am willing to give up a half or less MPG. Would be different for you all who tow less weight or less but we go to Arizona/Calif for winter and all over western Canada in summer.

 

Keep in mind that a particular speed, such as 60 mph while towing, and wind condition, and grade will determine the HP your engine has to produce. The HP required does not change when you shift gears. If you run higher rpm then the torque required goes down, but the HP required is the same. Same if you run lower rpm then the torque goes up and the HP remains the same. So there is no way to change the HP going through your transmission without changing the speed, grade, wind.

As the rpm torque combinations changes the engine efficiency changes though. In general lower rpm and higher torque will give you higher engine efficiency due to the throttle being wider open and the intake manifold less negative.

 

All above true, I have a scan guage and watching it and simple physics tells us that it takes a certain amount of horsepower to move a certain weight against wind resistance and drivetrain losses. Reason I use 4th is because I am moving nearly 16000 lbs and I know putting the power through a planetary will cause more wear on transmission than direct drive. If I was only towing the travel trailer I used to have before 5th wheel (approx. 5000 lbs) I would use 5th. Just putting in D and tow/haul I find it shifts up and down more than I like and doesn't gain any appreciable fuel economy. To each his own!

 

I can't stand it. You guys are so funny. So many facts my head is swimming. Good conversation guys. Thanks for keeping your cool.

I do want to comment on a couple of points.
When I owned my last RV which had a Ford Triton V10, I started searching for how to get the best mileage from it. I even called Texas where they are built and talked to a tech about the engines torque curve and where is the sweet spot to maintain the best power to RPM ration and so on. We talked about a lot of things including the useless cruise control. Two things to keep in mind. One, an internal combustion engine is just simply an air pump. Air and fuel in. Air and spent fuel out, (hydrocarbons and whatnot). 14.7% air to fuel ratio. More RPMs, more air pumped, the more fuel used. Less RPM, less air, less fuel. No way around it.
And two, physics works against cruise control. Cruise controls are just not that smart. They are run by a program algorithm which attempts to be as useful as it can be most of the time. Driving the motorhome I found that when running cruise on fairly flat interstate it worked OK but just a little hill and I would have to preempt the downshift by adding just a touch of accelerator until the TC unlocked and then turn cruse off and it would climb the hill with no further downshift. If I did not, it would unlock, downshift, and downshift again till it got back to speed. It's just psychics and a simple computer program which is not capable of being perfect in all conditions. What on this Earth is?

Peace Out!

 

One, an internal combustion engine is just simply an air pump. Air and fuel in. Air and spent fuel out, (hydrocarbons and whatnot). 14.7% air to fuel ratio. More RPMs, more air pumped, the more fuel used. Less RPM, less air, less fuel. No way around it.

Actually there are some ways around it. You are correct. The engine is an air pump. Pumping air takes a lot of power and contributes to the losses of the engine. When your intake throttle plate is near closed the intake manifold goes under a large negative pressure. To draw air in, the engine has to fight against that negative pressure. It not only has to compress the air up to 10 times atmospheric, it also needs to overcome the manifold negative pressure. For that reason engines are least efficient at low throttle openings. For maximum engine efficiency you have to get that throttle plate open and the intake manifold vacuum down. That is why running at lower rpm, higher torque, and more wide open throttle is more efficient -- generally speaking.

There are other ways of addressing the issue. The Atkinson cycle keeps the intake valves open longer thus letting some air back into the intake reducing pressure (but it costs HP). Or you can put a turbo on and the turbo pumps air into the intake, reducing manifold vacuum and air pumping losses.

The funny part is that those who put cold air intakes on their engines don't understand this. Cold air intakes use more dense air, so the throttle plate has to go further closed to maintain the correct air mixture, which in turn increases manifold vacuum and pumping losses. Cold air intakes reduce fuel economy, not increase it.