Transmission coolers

Submitted: Wednesday, Jan 10, 2007 at 01:09
ThreadID: 41051 Views:8499 Replies:10 FollowUps:0
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Hi Folks,

Could somebody explain in laymans terms the benefits of transmission coolers ( I have a V6 auto 90 series Prado towing a 1 tonne trailer ) and the long term consequences of towing without one.

Are transmission coolers readily available "after market", what sort of cost would I be looking at and how hard are they to install ?

Thanks in advance.

Cheers .... Taz
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Reply By: _gmd_pps - Wednesday, Jan 10, 2007 at 02:47

Wednesday, Jan 10, 2007 at 02:47
Transmission cooler is mounted in front of your radiator or on the side if space.
The transmission oil is pumped through and is cooled to cool down your transmission also. It is essential for towing heavy loads. I would not know anything about pricing or fitting on jap cars since mine comes with a transmission cooler standard. If you intend to tow a lot it will be worth it for the easier life of your transmission.

good luck
AnswerID: 214348

Reply By: Bonz (Vic) - Wednesday, Jan 10, 2007 at 09:19

Wednesday, Jan 10, 2007 at 09:19
Currently you will find that your transmission fluid is cooled thru the bottom of your radiator, so as well as the engine coolant your radiator cools your transmission fluid. Transmission fluid gets hotter than engine coolant so the radiator does a reasonable job

Its sort of like Framework 3 doing a word processing/spreadhseet/database job its passable but when the heat is on its found lacking.

Taking the tranny fluid cooling out of the radiator and putting it thru a seperate cooler especially when towing as the transmission and the engine work harder=hotter makes it easier (and cooler) for both coolants.

There you have it. You can get tranny coolers most places like Repco or Autobarn AutoPro Supercheap and the like. Piece of wee to fit.
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AnswerID: 214368

Reply By: Ian from Thermoguard Instruments - Wednesday, Jan 10, 2007 at 11:11

Wednesday, Jan 10, 2007 at 11:11
Hi Taz,

Automatic transmissions have a device called a "torque converter" between the engine and the main part of the auto gearbox, where the clutch would be in a manual. It's a type of fluid coupling, where a turbine on the engine shaft pumps oil (auto transmission fluid, ATF) to drive another turbine on the gearbox shaft. There's a third set of blades called the stator, which allows the coupling to multiply the engine's torque, often up to 2 times, when the engine shaft is running faster than the gearbox shaft (e.g. when accelerating).

Like all mechanical devices, torque converters aren't perfect, so some of the engine's power ends up heating the fluid. Older autos always had some 'slip', even when highway cruising. When towing, the amount of slip is higher, so more heat is generated. Sometimes more heat is generated than the standard cooler in the radiator can dissipate and the fluid overheats and breaks down, damaging the whole gearbox.

Most modern autos have a convert lock-up clutch which, as it implies, locks the engine and gearbox shafts together, eliminated slip, during steady cruising. But when towing in top or 'overdrive', sometimes the converter will never reach lock-up and again lots of heat is generated. That's why some manufacturers recommend towing with overdrive off or in 3rd gear with a 4-speed auto (as this allows the converter to reach 'lock-up' in the lower gear).

In any case, when towing there will be more slip overall than when driving solo, so an auxiliary cooler is often a good idea. However, some manufacturers do not recommend auxiliary coolers, so check with Toyota first, especially if still under factory warranty.

As mentioned, standard autos pipe their fluid to an oil-to-water cooler in the radiator. So it's usually a simple matter to fit an auxiliary cooler behind the grill and connect it in series. One of the original pipes is removed from the radiator cooler and hoses to/from the new cooler are attached in between. Like all such mods, it needs to be done with due care - if a hose slips off or rubs through, you’re in big strife!

Hope this helps. Ian
AnswerID: 214389

Reply By: banjodog - Wednesday, Jan 10, 2007 at 11:29

Wednesday, Jan 10, 2007 at 11:29
Most manufactures used to offer their own “towing kit” which was the towbar, wiring, plugs and transmission oil cooler if it was an auto – but I guess those days have long gone.

Cost is about $90 to $120 – but go for a good brand like a Davies Craig.

As already mentioned, most auto places will have them. Easy to fit so long as you can get to the pipes screwed into the radiator to fit the hose onto and remove the radiator grill for the cooler fitment. Two schools of thought whether to still use the radiator one or not with the external cooler.

Just have the correct transmission oil handy to top up once fitted – depending on the size of the cooler as to how much oil is required. Expect a bit of fluid to drain out too in the fitting process – always messy.

AnswerID: 214391

Reply By: Taz & Milka-Queanbeyan - Wednesday, Jan 10, 2007 at 13:57

Wednesday, Jan 10, 2007 at 13:57
Thanks for the simple explanations.

Cheers ... Taz
AnswerID: 214417

Reply By: Martyn (WA) - Wednesday, Jan 10, 2007 at 14:13

Wednesday, Jan 10, 2007 at 14:13
You could also run a better tranny fluid, the synthetics give up their heat a little bit easier plus they don't have have the same characteristics when it comes to air entrainment and foaming properties all which are killer for auto transmissions.
If you take the heat out you have to do it efficiently as mentioned before an auxillary cooler would be better than something that is only ever going to cool the fliud to somewhere around 70 degrees C, plus as also mentioned you need to consider warranty issues. Overcooling can be an issue, oil temp ideally should be around the 55 degree to 70 degree mark.

My opinions others may vary.
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AnswerID: 214422

Reply By: Peter 2 - Wednesday, Jan 10, 2007 at 14:54

Wednesday, Jan 10, 2007 at 14:54
Lots of late model vehicles run the trans fluid in the 70 -85 or 90 deg C range, anything over 100 is shortening the life of the fluid drastically, anything over 125 C is killing the trans.
It can be harder to fit aftermarket coolers to some vehicles as they use quick connect/plug in pipe fittings to connect to the radiator so normal hose barbs with pipe threads can't be fitted however the end of the tubes will take a rubber hose over the male fitting on the pipe. Always use the correct hose to connect the aux cooler, fuel line and heater hose is not good enough for the temps and pressures involved.
AnswerID: 214433

Reply By: Member - Jeff M (WA) - Wednesday, Jan 10, 2007 at 18:21

Wednesday, Jan 10, 2007 at 18:21
Yeah all that, and with the surf the transmision cooler (factory one) is a heat exchanger in the bottom of the radiator (bottom tank) so by installing an aftermarket cooler it also helps prevent the engine from overheating as the tranmission oil is cooler before it hits my radiator.

I've seen quite decent looking ones in auto shops for around the $100 mark. Should be very easy to fit (providing you can find the space!). Mine was already installed when I bought it, it sits behind the radiator between the rad and the viscous fan.
AnswerID: 214483

Reply By: awill4x4 - Wednesday, Jan 10, 2007 at 20:22

Wednesday, Jan 10, 2007 at 20:22
I have totally deleted the radiator auto trans coolers in my GQ and I am now using 2 front mount coolers in series. My normal running temps are 50C and even towing the caravan (approx 1.8 tonnes) in 38 degree heat last Saturday the temps never exceeded 85C and with it in 3rd gear with the torque convertor locked the cruising temps were 50-60C.
Regards Andrew.
AnswerID: 214511

Reply By: Member - SKI er (NSW) - Wednesday, Jan 10, 2007 at 21:07

Wednesday, Jan 10, 2007 at 21:07
Hi Taz,

Won't reiterate on the tec specs.

We recently fitted an external twin pair ofradiators for the transmission oil to a 1994 Pathfinder to be used for towing, on the recommendation of people on this site.

We couldn't be happier. The engine seems to be running much better and cooler, perhaps simply bcause the main radiator is being help a bit by the trans coolers.

AnswerID: 214531

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