Towing in overdrive - Diesel

[morrie Lurker Find all posts View Profile Close morrie]

Hi Morrie here, my very first post so please be patient with me. I have owned two Pardo's, both auto 3l turbo diesels and regularly tow a 14ft Millard caravan. I have always been made aware of porential gear box problems associated with towing in overdrive. I religiously towed in 4th gear in my previous vehicle however the technical advice I have been given suggests that overdrive can safely be used when towing on flat terrain with my current D4D Prado. I am a very fistidious owner and take pride in my vehicles, however I am still unsure of the advice I have been given and would greatly appreciate any feedback from your members. Many thanks Morrie.

[FlyNdrive Advanced Member Find all posts View Profile Close FlyNdrive]

Re: Towing in overdrive.

I was taught to never tow in OD as well. In college I worked in an auto shop that had a van towed in that caught on fire from towing in OD. The trans fluid boiled out and burst a hose. It was so hot it set the engine lining on fire and eventually the entire vehicle. Even if you tow for short distances it breaks down the transmission fluid and requires a flush ( speaking from experience here).

I hope this helps.

-Ben

[GDS Member Find all posts View Profile Close GDS]

Re: Towing in overdrive.

I have never owned an auto until I purchased the 120 six months ago. Nothing in the owners manual about this.

Love to hear other views on this one.

[Signature035 Advanced Member Find all posts View Profile Close Signature035]

Re: Towing in overdrive.

Hi Morrie,
Welcolme to pradopoint. There has been a bit oif discussion previously on this point and the general consensus is that it is fine to tow in Drive. I have towed my Jayco for the past 4 years behind my auto diesel and unless necessary, just leave it in drive...... never had any problems.

Heres one thread I found:

viewtopic.php?f=37&t=3926&p=93108&hilit=+towing#p9 3108

[Bushbasher Out of control poster! Find all posts View Profile Close Bushbasher]

Re: Towing in overdrive - Diesel

In my old 98 manual V6 I used to only tow in 5th with no head wind and on flat or downhill slopes with the aim of never allowing the car to "labour" and there never semed to be any real fuel saving by being in 4th or 5th.

Now, with my 09 D4D auto, I just let the electronic smarts take care of what gear to be in. With the car in drive and cruise control set it always gets better economy than I can by selecting gears and working the throttle.

The only damage will be done by towing beyond rated capacity. If the car is regularly serviced, and this includes keeping the radiator and cooling systems in good order, then there should be many years of trouble free towing.

Some auto owners have elected to install bigger trans coolers for the bigger towing jobs. You will find more on this subject elsewhere.

[dirttracker Senior Member Find all posts View Profile Close dirttracker]

Re: Towing in overdrive - Diesel

I have an '05 TD and tow a Jayco Outback Eagle. I find that I can leave to the auto to its business but the jump from 4th to 3rd is alittle harsh and noisy, so when a big hill is comming and I know that it will need to change down, I knock it out of 4th OD and into 3rd and the trans locks up and it pulls better and with 500 less rpm than jumping from 4th OD to 3rd proper. Of course I have the 4 sp auto not the 5sp.

regards
Martin

[ecka Lurker Find all posts View Profile Close ecka]

Re: Towing in overdrive - Diesel

Hi Morrie ( and others)

What an interesting range of opinions, as with most topics on this forum. I have been dragging a Cub camper (about 1200kg) with an 08 auto diesel GXL. I recall towing was discussed in several places in the "users' manual". But, they seemed to conflict, or I'm loosing it. So I contacted Toyota and got the following response.

"We do not recommend towing whilst the vehicle is in 'Overdrive'. Our recommendation is to drive using the "4" position (for 5 speed automatic models). The reason for this is when you are driving for long distances on a highway, if you were in the "D" position with overdrive ON the vehicle would automatically select gears depending on the driving conditions (ie. uphill, downhill, acceleration, deceleration, etc) and after time the changing of gears would eventually cause undue stress and strain on the transmission because of the extra weight you are towing. It is best to use the "4" position as this will create more of a constant cruising level without causing too many gear changes and leading to undue stress on the transmission.

The only exception to this rule is during extended periods of "hard towing", ie. steep hill climbing in 4WD, when "D" should be used to prevent causing severe damage to the transmission due to overheating.

Thank you for contacting Toyota and allowing us the opportunity to respond."

I thought this was interesting and wondered whether the same applied to driving in D with the cruise control on without the camper.

Cheers

[AJ120 Out of control poster! Find all posts View Profile Close AJ120]

Re: Towing in overdrive - Diesel

It seems the concensus here is that selecting drive and the auto changing into top gear, 4th or 5th depending on the model, means that the overdrive is on automatically. I have owned both model and it seems to me from looking at the rev counter that the 4 speed is 4 speeds plus overdrive so in fact a five speed and the same for the five speed which is in effect a six speed. i experimented with this only last week towing into a head wind, in drive the auto seems to drop back a gear (approx 200 rpm) if i then knock the lever into 4th it drops back another 300 rpm or so. this is why i think it five speed plus overdrive, so if you are driving with the gear knocked back to 4th or 3rd (depending on your model) you not only have the overdrive turned off but have changed back another gear as well. i tow a camper trailer weighing about 1200kgs when chock a block and on most occasions drive in D and have had no problems, also the 5 speed auto is a vast improvement over the old four speed, much smoother and better at selecting the appropriate gear when towing.

let me know if i am wrong about this.

cheers Andrew

[MickL Addicted PP Member Find all posts View Profile Close MickL]

Re: Towing in overdrive - Diesel

let me know if i am wrong about this

The shift in RPM you are seeing is the locking/unlocking of the torque converter, it locking up under cruise/low load conditions and eliminating the slip/losses of the torque converter increases fuel economy.


Overdrive is any gear that has a lower input rpm than output rpm (any higher than 1:1ratio and you are "overdriving" the output). This is in most cases the top gear in any gearbox, manual or auto.

Once you get past the 1:1 ratio of 4th in a 5 speed (or 5th in a 6 speed etc) there is a dramatic loss in torque (this is because while you have higher input rpm than output rpm the gearbox multiplies the available engine torque) however the mechanical structure of the gear means it's carrying a lot of load on it's gear contact points.

Think of your old ten speed bike as a kid: high gear = effortless cruising until you hit a slope or want to speed up then it's high load on your legs!...... low gears are easy on the legs but you have to pedal faster and burn more energy.

Sorry no extra gears... definately 4 in the 4 speed and 5 in the 5 speed auto, but both have a lock up torque converter.

Mick

[AJ120 Out of control poster! Find all posts View Profile Close AJ120]

Re: Towing in overdrive - Diesel

Thanks for that Mick

Cheers Andrew

[MickL Addicted PP Member Find all posts View Profile Close MickL]

Re: Towing in overdrive - Diesel

No worries Andrew,

There's always some confussion when it comes to "overdrives" as in the distant past most vehicles (especially comercial) had a 1:1 ratio top gear from the factory and an "overdrive" unit was something you could buy aftermarket and bolt to the back of your gearbox (with an extra gearstick to boot) to give you and extra "economy" gear ratio.

But as stated; and overdrive is actually any ratio with a higher output rpm than input rpm.

Also adding to the confussion is the "overdrive " button on some auto vehicles. This in fact not an extra gear but just changes when the torque converter locks up.


Mick

[Schaffer Addicted PP Member Find all posts View Profile Close Schaffer]

Re: Towing in overdrive - Diesel

"We do not recommend towing whilst the vehicle is in 'Overdrive'. Our recommendation is to drive using the "4" position (for 5 speed automatic models). The reason for this is when you are driving for long distances on a highway, if you were in the "D" position with overdrive ON the vehicle would automatically select gears depending on the driving conditions (ie. uphill, downhill, acceleration, deceleration, etc) and after time the changing of gears would eventually cause undue stress and strain on the transmission because of the extra weight you are towing. It is best to use the "4" position as this will create more of a constant cruising level without causing too many gear changes and leading to undue stress on the transmission.

The problem i have with this statment from Toyota is that in an Auto the gear selected is really the highest gear that the automatic transmission may enter. If you are in 5th as they suggest and start going up a resonably steep hill then the gear box would quite probably jump down to third or even second. I base these comments from an older 06 auto which does not have an overdrive but I could not see it working any other way since I have driven a few automatic toyotas and they all work the same.

[toddy Member Find all posts View Profile Close toddy]

Re: Towing in overdrive - Diesel

going on a little tangent... :wink:

MickL, my torque converter locks in about 84km/h on the speedo. Is this the standard speed? and also is it better to drive in this position (not towing anything)? I tend to speed up till it locks in and back the cruise down to 80km/h.

sorry for the questions still figuring out the prado, even though had it for 3 years :roll:

Cheers,

[MickL Addicted PP Member Find all posts View Profile Close MickL]

Re: Towing in overdrive - Diesel

MickL, my torque converter locks in about 84km/h on the speedo. Is this the standard speed? and also is it better to drive in this position (not towing anything)? I tend to speed up till it locks in and back the cruise down to 80km/h.

Toddy,

I can't answer your question with 100% certainty as my Prado is a manual. I would have assumed it would be controlled by the gearbox's computer and vary depending on load/throttle input?

It's a device designed to improve fuel economy so I don't see an issue with what you are doing...

It sounds like it's doing as it should, but if you think there's and issue I can certainly look into it for you and see what info I can rustle up.

Mick

[toddy Member Find all posts View Profile Close toddy]

Re: Towing in overdrive - Diesel

Mick,
Thanks for your response, nah there's no issue just wondering what it was also. I always thought it was a 5th gear but now I understand what overdirve means and such so thanks all in this thread, really informative.

cheers,