Towing without transmission cooler

[randog78 Junior Member Find all posts View Profile Close randog78]

We're towing a decent sized caravan (2360kg tare, probably around 2700 loaded) with a 2019 VX, but I have not installed a transmission cooler yet. Locking the transmission in 4th works well, no problem staying at 100 km/h and about 18 litres /100km. Two questions:

1. Is 6th the only overdrive gear or is 5th also an overdrive gear in a 6 speed transmission? (not sure how overdrive works so might be a noob question)
2. For occational towing of a heavy caravan is a transmission cooler a must-have?

Not surprisingly there are mixed and conflicting opinions out there and I expect nothing less here, but at least I would like them to be about my generation Prado in particular.

[gxl_d4d Advanced Member Find all posts View Profile Close gxl_d4d]

I have a similar setup as you (2019 car, towing similar weights). I don't believe a cooler is a must however it will increase the life of the gearbox if you can keep the temperature down. Heat hardens seals. I fitted a cooler somewhere between 30 and 40000km in preparation for buying a caravan. Fluid was dark brown but didn't smell. I've been dropping the fluid every 30 000km after fitting the cooler and it seems to stay red/pink with the cooler. I'm guessing the reduction in temperature is making the fluid last longer.

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

To answer your questions:

* Both 5th and 6th are overdrive gears (4th is 1:1 and 5th is pretty close to same ratio in both the 5 speed A750F and 6 speed AC60F gearboxes).

* The trans cooler is not a must have but recommended for towing/heavily loading up vehicle and driving over longer distances, and/or high ambient temps (also useful if doing lots of 4x4 hill work, sand driving, or doing lots of stop start as these also drive ATF temps up). The main heat generator in the trans is the torque converter when the clutch is not locked up so you using 4th will help with this as the pre 150kw ECM tends to take longer to lock the TC up and unlocks as soon as there is any load on the engine in overdrive. With cooler or not as you are towing worth servicing the trans (at a minimum) at the Toyota Additional Maintenance recommended 4yr/80,000 km intervals (covered in the back of your Warranty and Servicing Logbook).

Edit: Also worth getting yourself a Scangauge/Dongle with Torque Pro App or similar so you can monitor engine water temp, the trans temps, current gear and TC Lock status. As these will let you know if things are working OK.
* Water Temp should not go over mid 90s.
* Trans ATF Pan Temp you need to keep below 105 degs if possible (Normal range towing without a cooler is in 90s but higher than the 105 for short peaks on steeper hills is not a major issue).
* Trans ATF TC Temp will be same as Pan temp when TC is locked and rise sharply when the TC unlocks and you have your foot down. Shouldn't see above 125 degs but if it goes over 130 the ECM will start trying to manage by locking out overdrive and locking up earlier and in 3rd. At 150 deg it will put the A/T Overtemp warning light/message on so you need to stop and leave engine running until it drops back down.

[geo Junior Member Find all posts View Profile Close geo]

Good advice there from ptommo59.

Expanding on one piece of that advice:

When towing, drive with the transmission in the S position locked into 4th.
Don't tow in auto!

This makes a big difference to the transmission temperatures as it's not hunting up & down through the gears all the time.
It isn't the whole answer as a transmission cooler is still needed especially as you're towing a heavy van.

[404pug Avid PP Poster! Find all posts View Profile Close 404pug]

Heavily laden for remote outback and with roofrack with 2nd spare, maxtracks and awning, the gearbox performs similar to what it does towing. If left in drive at 110 kph temps will climb into the 120s . A change to S4 will see them quickly into the 90s where they will stay. Fluid was changed 5000km ago at 80000 and was still OK but was just starting to change colour. It is annoying to have to manage the gearbox this way but obviously Toyota doesn't see the high temps as a major issues if you change fluid at 80000 km. Interestingly I was told by the Toyota service department in Alice Springs 6 months ago that they have never seen a problem with the 6 speed auto in Prados, Hiluxes or 200series. Many of these cars are well flogged fleet cars operating in months of 40 deg plus temps. As said above get a scanguage or similar, tow inS4, and use 5th and 6th downhill or with strong tailwind when towing. 2016 model

[watsea Member Find all posts View Profile Close watsea]

I have a 2019 GXL and tow a 2.7t van, so similar to Randog78. Sounds similar performance too.
I have not fitted a transmission cooler but rather getting the transmission serviced at near 50k km intervals. I am currently on trip and had the second service done at 90k km. I would think a cooler would be a good idea however, warranty issues are a concern for me. Because the vehicle is for private use (ie not commercial), it has an unlimited kilometre warranty on the engine and drive train, for seven years, if the vehicle is properly maintained. A Toyota rep claimed that Toyota did not recommend transmission coolers as Toyota claim the coolers increase pressures within the transmission. That would be true because of the extra piping involved in getting fluid to the cooler and within the cooler itself. By how much, probably not much, but maybe Toyota could use that point to disallow a warranty claim on the drive train, if an event in the transmission occurred.
During towing the van, I select S4 mode for normal, For steeper inclines, I manually select lower gears while in Sports mode. I use an app which monitors the transmission temperatures, and gear selected, and a few other things. (Thanks Pradopoint members for helping me with some of the formulas).

For my vehicle, I find that selecting Cruise Control while in S4 mode, gets the transmission to lock the torque converter more easily. While in Cruise Control, it tends to hold the lock for a bit longer in S4 while going up slight inclines. Things can get a bit mixed, if at a higher speed and Cruise Control is left activated.

Also, while towing, if in S4 or a lower gear, the diesel engine has more rpm, (not necessarily less fuel efficiency) and thus the coolant and exhaust manifold temperature are lower which is better for the motor.

[randog78 Junior Member Find all posts View Profile Close randog78]

This was the sort of stuff I was hoping for, appreciate every single reply.

I've got an ODB2 scanner somewhere, so I will dig it out and keep an eye on the temps. If I fit a transmission cooler I will see if I can get some sort of written approval from my Toyota service department because I have kept up with their service intervals so far and made sure I still qualify for the 7 year unlimited kms warranty. The car has only done 65 000 kms, so if something goes wrong at this point they might look for any way out of responsibility. It's due for it's 90 000 km service in a months time, I will ask them to check the transmission oil then as we are doing a 3000 km trip for Easter first.

Cheers!

[gunda Member Find all posts View Profile Close gunda]

I have a MY21 Kakadu and tow a compact van (Karavan) with a tare of 1800 and travel weight in the 2300-2400 range. I have not fitted a transmission cooler, yet. I have a Scangauge II. The newer transmission locks very well, and I can tow in S5 on flat or moderately undulating country without any hunting and with stable transmission and transfer case temperatures. It is important to switch to S4 in advance when a steeper hill approaches, and S3 or lower for very steep hills. The key is to switch in advance and not let the transmission struggle before downshifting. On very flat territory I can lock in S6 at around a true 100kph with stable temps.

However long, steep winding climbs can elevate the ATF temp, esp the transfer case. It's the slowing for corners and then speeding up again that heats things up. If I can maintain speed then things are generally manageable, but that means not too many sharp corners. On a recent trip over a lengthy, undulating, rough dirt road the temps got a fair bit higher than I'd like for longer than I'd like. The rough country meant that maintaining speed uphill simply wasn't possible.

This experience had me reconsidering a tranny cooler, My problem is that the Kak has no spare payload when it and the van are fully loaded for travel, so I have been very reluctant to add all the usual outback touring extras. 404pug's comments from the Alice Springs dealer are reassuring, and certainly the six speed box with the 150kw engine does seem like a robust combination. Watsea's point about the seven year transmission warranty and a cooler are also well taken, perhaps I could consider it then.

I regard a Scangauge as essential if you're towing. At the very least you need to know how hot things are getting. You learn from watching the gauge how to maintain temps by driving smoothly, which I suspect also improves fuel consumption. I only tow [edit - this originally said in D, which I never tow in] using cruise control on flat, straight terrain. It does make life easier on the Hay Plains for example, at the cost of a slightly higher ATF temp,

[Not Enough Time Junior Member Find all posts View Profile Close Not Enough Time]

Thanks to Randog78 for asking this question and for the various responses.
It is a question that I should have asked earlier for my 21 GXL which tows a 2.2T (Gross/ATM) Hybrid van. I've been reluctant to buy a Scangauge (just one more thing to monitor).
I've been towing in S4, I've had no adverse comments from dealers following services (up to 100 000km) re Trans Oil colour. Seems I'll just keep doing that as the slightly more adverse fuel consumption in a lower gear is way better than a new transmission.

[randog78 Junior Member Find all posts View Profile Close randog78]

Seems I'll just keep doing that as the slightly more adverse fuel consumption in a lower gear is way better than a new transmission.

I got about 18 litres/100km on two 3 hour highway drives, and I haven't heard about anyone getting any less than that so far regardless of locking in 4th or leaving it in auto. So I guess the fuel consumption isn't affected, but strain on the transmission definitely is.

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

Its funny when Toyota reps make claims like Watsea posted "Toyota did not recommend transmission coolers as Toyota claim the coolers increase pressures within the transmission".

There is no way a correctly installed secondary transmission cooler can damage an Automatic Transmission unless there is an oil leak and drains the trans or a complete blockage which will cause the trans to eventually overheat (both issues can happen with or without a secondary cooler).

There are regulating valves for trans oil pressures and if the pressure goes out of acceptable range the shift quality and torque converter operation will be affected and the ECM will detect this and trigger various DTCs and potentially limp mode to protect the trans (so increased pressure as a reason for not recommending secondary coolers or rejecting a warranty claim is a furphy).

The only downside to a secondary cooler is the additional time the ATF takes to get up to operating temps which affects shift quality and fuel economy as the ATF lubrication qualities are below optimum levels for longer, particularly in colder climates (the Toyota WS ATF fluid is used as it has better low temp performance than earlier Type 4 ATF and maintains its properties longer in-service so given the Long Life fluid tag)

[gunda Member Find all posts View Profile Close gunda]

I got about 18 litres/100km on two 3 hour highway drives, and I haven't heard about anyone getting any less than that so far regardless of locking in 4th or leaving it in auto. So I guess the fuel consumption isn't affected, but strain on the transmission definitely is.

Admittedly the Karavan is easy to tow and lower profile that many vans, but even so with a GCM of around 5.2t my MY21 typically gets in the low 13s / 100kms on the open road, and occasionally less than that. It only gets over 14 with sustained climbing or winds or stop-start driving, and over 15 is fairly rare.

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

I tow a full height offroad van which weighs just over 2600kg (ATM 2800kg) with a GCM at that weight of 5320kg.
I usually sit around 95 km/hr in S4 or S5, at that cruise speed I average 14.4 L/100km. The only "performance" extra is a MM4X4 Lock up kit which works very well.

Personal experience has shown anything over an indicated 100 km/hr cruise markedly increases fuel consumption even when not towing.

My MY18 Prado is lifted 50mm with ARB bar, roof platform and running extra load Yoko GO15's which all contribute to fuel consumption especially over that magical 100 km/hr mark.

Lee

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

I posted on here a while back but for those with a Scangauge or Torque Pro/Car Scanner etc you can access the ECMs estimate of the condition of the ATF via the ATF Thermal Degradation Estimate parameter (The Toyota listed upper threshold for ATF still useable is 49999 and needs to be reset each time you service the trans using techstream).

It would be interesting to get an idea of what sorts of numbers people are seeing at various kms and with/without coolers fitted.

I know there will be lots of variance in usage which will affect these but still may be an interesting exercise to get an idea of the spread, so if you are interested see what yours is atm and post on here (will get mine today and do this).

The codes for the 150kW 1GD are below but haven't located the 130kW version as yet (For Prado/Hilux/Fortuner this is only available on the AC60F 6 speed models).

Scangauge:

TXD: 070022162B
RXF: 04620516062B
RXD: 3010
MTH: 000100010000
Name: ATD

Torque Pro / Car Scanner

Mode/PID: 22162B
Long Name: ATF Thermal Degradation Estimate
Short Name: ATD
Minimum Value: 0
Max Value: 65535
Scale factor: x1
Unit Type: Est
Equation: INT16(A:B) or 256*A+B
OBD Header: 0700

[randog78 Junior Member Find all posts View Profile Close randog78]

ptommo59

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ptommo59 I was going to try to find this information, so thanks for posting!