Thread: Max D4 SDV6 safe transmission and coolant temperatures while towing

I have fitted an additional tranny cooler and have an "Engine Watchdog" gauge as well as a "Scanguage" fitted to monitor what's going on. I have a 3.3ton van that I have towed to Adelaide through 43 degree heat at Broken Hill several weeks ago, I constantly monitor what is going on with my car and adjust my driving style to suit the conditions prevailing. This last trip I had a strong headwind on the SA border down to Adelaide so I dropped from my normal 93-4kph down to 84-5kph to keep engine temp around 100-105 and tranny below 100.

I have removed anything in front of the radiator that can divert the airflow (lights and winch control) as I found this to have the greatest affect on temp of engine or transmission. I once tried towing the van up the Toowoomba range in low range, it was a disaster, I pulled over and let it idle for 15-20min to get it to a reasonable temp, then set off in high range up to the legal 60kph and after that the maximum temp was 107-8 from memory.

My 2005 D3 has 313k and has towed the van 150 to 200k.

Ryall

Ryall, have you ever risked it and run at 110 degrees? Felt the thrill of it? I went to 120 once and my god, it was like being on crack. You should try it - you haven’t lived until you do.

I owned (I’ll admit it) an MY14 Grand Cherokee, which has the 8 speed ZF box. Jeep had installed a separate trans cooler standard to this model.

When I owned it, it ran at 93 (normal) and 96-98 (towing).
I don’t know what the D4 runs at. I reckon into the low hundreds wouldn’t be a problem.

Originally Posted by DiscoJeffster

You actually run the risk by using a separate cooler of not getting the oil up to it’s designed operating temp and doing more harm. Cold oil isn’t good necessarily good oil.

I used to believe this also until I read an excellent writeup by a Ford transmission engineer that categorically debunked this complete with comprehensive thermocouple data. Once I read it, it made complete sense. I'll have a look and see if I can find a copy.

The in-radiator transmission cooler sits in the cool side of the radiator, or the transmission cooling flow (for an in-transmission water cooler) always comes from the cool side of the radiator.

This is *always* cooler than the fluid coming from the transmission, even just after startup. Think about it. The radiator gets heated by the engine via the thermostat. So the fluid in there is at ambient up until the engine is warm enough to even open the thermostat. Then it's bleeding coolant into the hot side of the rad. By the time it gets to the cool side of the rad, its considerably cooler. The radiator cooler *never* heats the transmission fluid under any circumstances. Remember the fluid entering the cooler is the hot fluid straight out of the torque converter, not the cooler bulk oil in the sump.

The fluid/fluid heat exchangers are also considerably more efficient from a surface area perspective, so they are sized as required (relatively small). It takes a considerably larger air/oil cooler to effect the same cooling as the in-rad unit. Best effect for an add-on is to fit a smaller air/oil transmission cooler in series with the in-radiator cooler depending on your specific deficiency to either pre-cool the fluid entering the radiator or supercool the liquid leaving the radiator. As any heat exchange is based on the log mean temperature difference over the two sides, you'll always get best bang for your cooler area by using the air cooler to take the hot fluid straight from the transmission. On the cool side you'll need a much bigger HX to remove the same amount of heat.

Hey Brad. Thanks. You know I started to think along these lines myself as to what temperature the bottom of that rad is - Eg how much temp reduction happens from top to bottom. Also was going to review if there’s any thermostat control.

Until two weeks ago ive never heard of a transmission cooler as an after market necessity.

Later this year year I will be travelling for six months around the eastern half of Aus towing a 3.2ton off road (ie high) caravan. We’ll be spending three months of that in the top end and up the middle from Adelaide to Darwin so I’m expecting hot temperatures.

I see above Riley has fitted this to his D3 but has anyone fitted one to a D4? Or felt the need?

trying to avoid the above - she’ll be right approach but also keen to avoid unnecessary costs and changes to the car. If anyone can lay it out for me straight

its a 2011 d4 - 2.7L

Originally Posted by Lukeis

trying to avoid the above - she’ll be right approach but also keen to avoid unnecessary costs and changes to the car. If anyone can lay it out for me straight

Back before the invention of lockup converters an auto towing generated a *lot* of heat. Provided you can keep the trans locked up they just don't generate the heat they used to as the converter is really not doing much other than sloshing some oil around. Put the boot in going up a hill and drop it out of lockup though and you might need to get rid of some extra heat.

Heck, if I tow the van in my 4 cylinder auto Volvo (which only locks up in 4th) and don't go fast enough to get it to lock up, even *with* an aux cooler I can see trans fluid temps > 130C going up any sort of grade. If I can get it to lock up that drops to about 105C.

I'm led to believe the ZF boxes are pretty impressive about how little energy they burn as heat, but if I had an auto Disco (which I don't) and towed a 3T+ van (which I don't), I'd probably be either looking for an aux cooler *or* changing fluid more frequently (or at the cost of ZF fluid probably getting it tested). Heck, my D3 which was specced for "Tropical countries" has a factory fitted aux cooler on the post-radiator coolant going to the *fuel* cooler. None of the landrover places I spoke to had ever seen one, let alone knew where to get one. Yay for LR-Direct.

Towing is so intense for the box, it’s unsurprising that so many fail before the standard 230,000km claimed interval, but to be fair, LR does state that towing is arduous use and means additional changes. Unfortunately the dealer doesn’t know what you do with it between services so doesn’t prompt.