Dual clutch transmissions, towing and heavy-duty uphill reversing

Steep driveways and reversing a trailer: Will you kill the new eight-speed dual clutch transmission in the new Santa Fe and Sorento diesel AWD models?

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If you’re in the market for a new large SUV, specifically the new Hyundai Santa Fe or Kia Sorento, but you need it for frequent moderate towing and have concerns about its transmission - allow me allay those fears.

Here's the question from Larry the landscaper: 

Good question. At the time I did so wish I had a good answer, so the lapsed engineer in me, which still recoils at the prospect of making stuff up, stalled for time and asked for more info from Landscaping Lazza.

He deployed his protractor and tape measure (and his smartphone).

As you can see, it’s a pretty steep driveway, but not that long. I can empathize. About 20 degrees, 21 metres, and the trailer might weigh 400 kilos on a heavy day. And Larry reverses in at the end of the day, five days a week, after toiling hard, turning busted-arse Sydney scrub into the cover of Home Beautiful, repeat.

Because I had no idea about the duty cycle for this new transmission, I reached out to Kia’s top engineering dude in Australia, Roland Rivera and he reached up to Hyundai/Kia HQ, where the R&D brainiacs hang out, in a very cool place called Namyang.

Everyone should go to a place like Namyang, once in their lives - just for the test tracks and the wind tunnels and the anechoic chamber and the rooms where they bake, freeze and break various parts - and whole cars - with great precision. They take this stuff very seriously.

I’m sure there was some brow-furrowing up there on this. Like: ‘He wants to do what?’ Anywho, Namyang dudes give Lazza’s driveway and trailer due consideration, then they go (I’m paraphrasing):

That should be fine, dude. Just make sure he does it one-up. Like, get the passengers (if any) out.

Pro tip: Do try to avoid hill-holding using the throttle and slipping the clutch - because in the domain of transmission good things and transmission bad things, that’s generally bad.

They also go (again, paraphrasing): this is a relatively severe operating condition, because of the low speed and low airflow and high load from gravity and therefore high input heat and low forced convective cooling effect - even though the clutch system is wet and features a dedicated cooling system.

Furthermore, the clutch system features self-protection. And if that triggers, the clutch is programmed to release at a pre-set temperature, to prevent serious damage. In other words, ‘we did our best to idiot-proof things - even though humanity always invents a better idiot when we do that’. 

And if that happens (the thermal protection clutch release trigger) you will lose tractive effort, so wait a couple of minutes, dude, and leave the engine running (presumably to maintain oil circulation through the cooler). Then you can go again.

I must say, this all seems quite reasonable to me. But the variables are, obviously, how often you do it, how steep and long is your driveway, how heavy is your trailer, and how capable/mechanically sympathetic are you, as the driver.

USEFUL LINKS FOR TRANSMISSIONS & TOWING

Anatomy of a Holiday Towing Disaster: How you can prevent one >>

Epic Towing Disaster Q and A: Your trailer crash feedback >>

The truth about servicing automatic transmissions (even the sealed ones) >>

Heavy towing with automatic transmissions: what not to do >>

Ultimate Transmission Guide: Manual, Auto, Dual-Clutch and CVT >>

Complete heavy towing guide: GVM, GCM, payload, towball limits explained >>

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Double Checking

While all this was happening I also reached around to the dudes at Hyundai Australia, because I anticipated getting enquiries about the Santa Fe about reversing trailers uphill.

While Sorento and Santa Fe are identical in the powertrains, the two operations have separate engineering departments here in Australia. So I reached out to Hee Loong Wong (general manager of product engineering) who, I’m paraphrasing, says:

Yeah dude, the 8spd DCT has a liquid reservoir that runs through an oil cooler, somewhat like a convention hydraulic auto, but it is dedicated to the wet clutch only, so the fluid is not shared with the transmission’s gearset.

This cooling system makes the transmission quite durable.

I’m thinking this cooling arrangement means fragments in the cooling oil, if any, from clutch wear over time, don’t get into the valve bodies or filters in the gearbox. So that’s a bonus.

Wongy further opines there are limits to anything, and of course, if you put a 2000kg caravan behind a Santa Fe diesel and you stall it out on purpose using the throttle on a steep driveway, it won’t be long before you engage the thermal protection system and disengage the clutch, thereby saving it from any further lack of mechanical empathy on your part.

Wongy also says a half-tonne landscaping type trailer would not be an issue in these circumstances, unless of course you’re deliberately abusing it.

I tried recently to invoke the thermal protection on a Santa Fe Elite diesel on my own driveway from hell, which is much like Larry’s driveway, only twisty which means inevitably slipping the clutch somewhat in order to go slow and not hit anything.

You can watch that report here: 2021 Hyundai Santa Fe dual clutch transmission extreme endurance test >>

Alternatively, if you just cannot stomach the idea of using the DCT in this way - or if you’re likely to abuse it by reversing up the North Face - you could just opt for the V6 with a conventional epicyclic torque converter automatic transmission.

In Moderation

I’m quite confident in both these vehicles (Santa Fe and Sorento) if you plan to do this kind of uphill trailer reversing activity, and I base this conclusion on having tried to do get that transmission to overheat myself.

But I did this activity without trying to abuse it. Anything mechanical can be damaged very easily when you deliberately try to abuse it and try hard enough. And I know how to break stuff.

I also draw this conclusion from having two confirmations from two highly qualified engineers whom I respect in the industry, who have runs on the board and didn’t baulk for a second when I asked them this question. Those engineers were also willing to be quoted and put their reputations on the line when giving me the thumbs up. I didn’t even need to deploy my cattle prod.

I hope this helps if you’re in the market for a new SUV.

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