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  1. #1
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    Default Automatic gearboxes and towing heavy loads

    My take on it is that really the gearboxes and the electronics that make them work are smart enough to make the right decisions given the circumstances. And if those circumstances include a heavy load and a heavy trailer (then add up a hill, down a hill, round a bend, along a straight, starting and stopping in town, etc.) I am inclined to leave it to do its own thing.

    Yet some on the internet seem to indicate drivers should opt for manual mode, and steer clear of using 6th gear (or 8th - the highest gear). I find this strange.

    Are we to make executive decisions on behalf of the engineers who designed it all, or can we leave them to get us to our destinations in the most efficient way?
    Last edited by williepvjr; 2021/09/20 at 09:27 AM.
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  3. #2
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    Default Re: Automatic gearboxes and towing heavy loads

    When towing a heavy load with an automatic it is easier to do a manual section due to the fact that you are able to control the speed easier, exactly 1the same as when towing in a manual vehicle. If one was to leave it in D and let the box kick down once on the hill, you have already lost some momentum and the gearbox will quickly have too change down another gear. I have never avoided towing in top gear when the load allows.

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    Default Re: Automatic gearboxes and towing heavy loads

    I tow heavy loads (2 to 3 ton) quite often and on extremely challenging uphill areas I tend to shift myself as the auto box does not always adjust to the conditions as quickly as needed. Also to gear down again to reduce pressure on the brakes on longer and steeper downhill sections.

    That said, as a rule, I just leave it in sport mode whilst towing 95% of the time. The auto box does do its job pretty efficiently.
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    Default Re: Automatic gearboxes and towing heavy loads

    I turn the "Over Drive" off, with the button on the gear lever, this eliminates unnecessary gear shift and the gearbox stays/holds longer in the gears. I find it very convenient.
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    Default Re: Automatic gearboxes and towing heavy loads

    Although I have not towed above an estimated 1.6 ton I normally manually select 5th in the Hilux to stop it selecting 6th and running at around the 1500 - 1700 RPM mark. I don't have an EGT gauge, but gut feeling is that I'd rather use a little bit more diesel than possibly damaging the engine, especially in hilly country or when the wind is a real problem.

    But having said that, should the ECU not be clever enough to protect the engine, gearbox. etc?
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    Default Re: Automatic gearboxes and towing heavy loads

    I towed my camping trailer (max 800kg, but high wind resistance) with my 3.2L Everest. Cruised at 110km/h with cruise control. Drove in D most of the way, and switched to S when the going got a bit hilly or when I needed to pass. Never manually changed it. The gearbox tend to shift back a gear a bit earlier in S-mode, and thus keep the revs a bit higher, exactly what I needed. Engine temp on inclined vs flat deviated by 4 to 5 degrees C. Did almost 4000km, no problems at all.

    I am also of the opinion that modern auto boxes had the AI to preserve itself well enough in all circumstances.
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    Default Re: Automatic gearboxes and towing heavy loads

    Quote Originally Posted by mplester View Post
    If one was to leave it in D and let the box kick down once on the hill, you have already lost some momentum and the gearbox will quickly have too change down another gear.
    I'd agree with a pre-emptive downshift approaching an incline.
    Last edited by williepvjr; 2021/09/20 at 10:21 AM.
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    Default Re: Automatic gearboxes and towing heavy loads

    Quote Originally Posted by williepvjr View Post
    My take on it is that really the gearboxes and the electronics that make them work are smart enough to make the right decisions given the circumstances. And if those circumstances include a heavy load and a heavy trailer (then add up a hill, down a hill, round a bend, along a straight, starting and stopping in town, etc.) I am inclined to leave it to do its own thing.


    Are we to make executive decisions on behalf of the engineers who designed it all, or can we leave them to get us to our destinations in the most efficient way?
    Quote Originally Posted by CornellMans View Post

    I am also of the opinion that modern auto boxes had the AI to preserve itself well enough in all circumstances.
    I suppose it depends on the definition of modern, and what the intention of the programming is.

    My 2012 (modern??) V6 Hilux with an electronic gearbox is programmed for fuel efficiency (decision of engineers??). As such, it will change up as soon as it can and hold the higher gear, even if it means unlocking the torque converter. So when towing, it will stay in 5th, and slip the torque converter. I have seen ATF temperatures approaching 110 deg c before I manually had to select 4th to get the torque converter to lock up and cool the ATF.

    To be honest though, the gearbox will try to protect itself by gearing back and illuminating the ATF temp light, but I think that happens in the 140 to 150 deg c range, which I feel is too late, considering, as I understand it, ATF begins to degrade @ 120 deg c.

    So to my view, sometimes the electronics are not smart enough but perhaps that is due to design.

    That is why when I tow, I tend to lock my vehicle into 4th, the ratio closest to 1:1.
    Last edited by Rookie; 2021/09/20 at 10:47 AM. Reason: detail added
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    Default Re: Automatic gearboxes and towing heavy loads

    Quote Originally Posted by CornellMans View Post
    Drove in D most of the way, and switched to S when the going got a bit hilly or when I needed to pass. Never manually changed it.
    I like the logic.

    Id prefer to do a manual downshift than selecting Sport... While it will remain in lower gears for longer I am unsure that there would be a change in the shift itself that would not be suited to towing conditions. (Maybe someone knowledgeable on the ZF 8HP in Land Rovers could enlighten us on the Sport mode).
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    Default Re: Automatic gearboxes and towing heavy loads

    OK - my experience with auto boxes may be a bit out of date.
    Take it from whence it comes:

    My last auto box experience was with my Ranchero Outback 4L straight six with fuel injection and engine management control (computer), four speed auto box, hydro-track , etc. with different change ratio settings (sport vs economy).
    And and also similarly the Opel 3.8i Auto that I had before the Ranchero.

    In those days I towed mainly conventional caravans. And SWAMBO knew how to LOAD them, so ja.
    Since then the Manual Isuzu KB only.

    Back to the auto box issue:
    What I found with both the Ranchero and the Opel was that those auto boxes were good at protecting themselves by changing gears but in hilly / mountainous or sudden short inclines would do so too late ... then losing momentum and having to change even lower down.

    So I used to tow in auto on level stretches or at higher speeds but when going slower in undulating, sandy or muddy conditions I would override to manual selection because I could see the terrain and conditions ahead and so be pro-active in gear selection whereas the auto box was reactive.

    Maybe the newer vehicles can anticipate the terrain not yet encountered - nothing amazes me anymore.
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    Default Re: Automatic gearboxes and towing heavy loads

    I believe the conventional wisdom when towing with an auto box is to tow in the gear that is closest to a 1:1 ratio.

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    Default Re: Automatic gearboxes and towing heavy loads

    Quote Originally Posted by Andrew Leigh View Post
    I believe the conventional wisdom when towing with an auto box is to tow in the gear that is closest to a 1:1 ratio.
    I think that believe comes from a time when manual gearboxes tended to strip the high gear due to labouring. In a manual car you are the brain, in an auto there is an electronic brain that will prevent you from using too high a gear for the situation.
    ....

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    Default Re: Automatic gearboxes and towing heavy loads

    Having only towed with manuals until a year ago, I just leave it in D and go.

    If I feel the engine laboring on a slight incline I just press harder on the go pedal to let the box click down once and all is good again.

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    Default Re: Automatic gearboxes and towing heavy loads

    Quote Originally Posted by williepvjr View Post
    My take on it is that really the gearboxes and the electronics that make them work are smart enough to make the right decisions given the circumstances. And if those circumstances include a heavy load and a heavy trailer (then add up a hill, down a hill, round a bend, along a straight, starting and stopping in town, etc.) I am inclined to leave it to do its own thing.

    Yet some on the internet seem to indicate drivers should opt for manual mode, and steer clear of using 6th gear (or 8th - the highest gear). I find this strange.

    Are we to make executive decisions on behalf of the engineers who designed it all, or can we leave them to get us to our destinations in the most efficient way?
    The Toyota engineers actually tell you (In the Hilux Manual) that when towing you should use S4. I think if you tow 3.5 tons as allowed by Toyota (but not legal in SA on a Hilux) one should stick to that advice. But towing say 1.6-2.0 ton on nice roads, limiting speed to 100-110, S5 works well.

    The Hilux actually also gears down on downhills if cruise-control is set.

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    Default Re: Automatic gearboxes and towing heavy loads

    modern autoboxes monitor a range of inputs to determine ideal gear, and that includes, speed, RPM, throttle input (i.e. torque demand). The engineers have determined the acceptable range of parameters for each gear so just stick it in D and forget about it, if you feel its not gearing down fast enough for your liking then stick in an S and forget about it. The only time to use manual mode is to take advantage of engine braking on long descents.
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    Default Re: Automatic gearboxes and towing heavy loads

    Quote Originally Posted by IcePick88 View Post
    Having only towed with manuals until a year ago, I just leave it in D and go.

    If I feel the engine laboring on a slight incline I just press harder on the go pedal to let the box click down once and all is good again.
    That's where "sport mode" is useful - Kicks down sooner, but in my opinion still too late.
    Already taking strain - that's why I prefer pre-selecting manually.
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    Default Re: Automatic gearboxes and towing heavy loads

    Quote Originally Posted by mullerza View Post
    so just stick it in D and forget about it, if you feel its not gearing down fast enough for your liking then stick in an S and forget about it.
    In your X3 M40i, switching it over to sport, does it not change the speed and nature of the shift? In my little 1 series the physical difference in the shift itself (not just holding gears longer, but the physical action of going from gear x to y) feels so extreme in comparison to comfort mode that I'm concerned that if it is the case that a similar difference is built into my Range Rover it would just mash the box to bits while hauling 3.5 tons.

    It seems fine to do a pre-emptive downshift on the paddle here and there, and then the rest of the time leave it in D.

    I'm not yet sold on using S.
    Last edited by williepvjr; 2021/09/21 at 11:20 AM.
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    Default Re: Automatic gearboxes and towing heavy loads

    Quote Originally Posted by Tom13 View Post
    I think that believe comes from a time when manual gearboxes tended to strip the high gear due to labouring. In a manual car you are the brain, in an auto there is an electronic brain that will prevent you from using too high a gear for the situation.
    I would also think that the Fluid coupling nature of current auto-boxes would reduce impulse impact damage being transferred through the Gearbox.

    This obviously isn't the case in a DSG gearbox, but I don't think these are typically employed in the standard tow vehicle.

    Protecting the auto-box is probably not the main reason for downshifting for an incline, but rather to maintain momentum as you would prefer to be in the correct gear for the worst of the incline, or at least minimize the amount of shifts while climbing.
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    Default Re: Automatic gearboxes and towing heavy loads

    Quote Originally Posted by williepvjr View Post
    In your X3 M40i, switching it over to sport, does it not change the speed and nature of the shift? In my little 1 series the physical difference in the shift itself (not just holding gears longer, but the physical action of going from gear x to y) feels so extreme in comparison to comfort mode that I'm concerned that if it is the case that a similar difference is built into my Range Rover it would just mash the box to bits while hauling 3.5 tons.

    It seems fine to do a pre-emptive downshift on the paddle here and there, and then the rest of the time leave it in D.

    I'm not yet sold on using S.
    No difference in the nature of the shifts on the X3, or the previous Q7, Touareg or Territory. Switching to S changes how soon the car will downshift and how long it will hold the gear. Maybe because it shifts so much sooner it feels like a harder shift?

    Towing heavy loads requires a more gentle approach to everything including the throttle, just mashing the loud pedal and letting the box sort itself out is also looking for trouble.

    On all the above cars (except X3 as I havent towed with it yet) I found the best approach to long distance towing is to stick in D with the cruise control on and let the car sort itself out. Obviously this only works if you have ample power relative to the load being towed .
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    Default Re: Automatic gearboxes and towing heavy loads

    My personal opinion:
    Not all gearboxes were created equal and not all driving styles and loads are equal. Bad or "inconsiderate" driving habits won't break your gearbox or engine, it is just placing unnecessary strain on a very expensive piece of equipment that may only bite the next owner.
    1) understand your gearbox. Observe when the lock-up clutch locks and unlocks.
    2) understand and monitor your gearbox oil temperature fluctuations.
    3) be aware of unnecessary gear shifts - up and down.
    4) be aware of EGTs.
    When I tow our Echo Chobe, the preferred cruise speed is 100 - 110km/h for comfort and safety reasons. I always use cruise control - I'm addicted. At that speed I'm right there where 6th gear comes into play. If I leave the box in auto, 6th gear will be in and out the whole time. Also, the engine spins at only 1600rpm in 6th, which I consider too low for high loads.
    I thus lock the box in 5th on the open road with the van in tow. I really enjoy the smooth, quiet and effortless operation of the engine at just over 2000rpm. Only mountain passes require input on the gearstick.

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