There’s no doubt that automatic vehicles are becoming more and more common. This applies in the 4WD world too; there are very few 4WD’s that come out of the factory in a manual only option, with a large majority of those sold being automatics.
They offer a huge range of benefits, but at the end of a day are a more sophisticated bit of equipment, and need to be cared for a bit differently to a manual gearbox. I’m told that 95% of automatic transmission problems stem from the oil running too hot inside your automatic box, and this is a problem that can be easily remedied.
It’s imperative that you take good care of your automatic transmissions, as they are expensive, sensitive and can cause you a huge amount of trouble when things go wrong.
Automatic transmission temperature monitoring
I suppose the first question to ask is whether or not you are aware of the temperatures inside your automatic gearbox. If you run an older 4WD, the only way you can do this is with an aftermarket temperature probe.
However, all new 4WD’s come with OBD2 ports, and they also have transmission temperature transducers mounted as factory. Now, as a normal user, you won’t see this – the reading is sent to your vehicles ECU, and as long as it doesn’t go above a set temperature you are none of the wiser.
If you do get the box hot, and often this is VERY hot, a light will come on the dash telling you to pull over and let it cool. In most cases if it gets hotter than this the vehicle will go into limp mode and you’ll have the power cut.
With the addition of OBD2 ports in modern vehicles, you can get gauges that plug in and will read what ever your ECU has access to. We run the Ultra gauge, and have programmed the little code in needed to read the transmission temperature, and as a result can see it live while driving along.
If you are worried about your transmission temperatures, this is a good place to start; the Scan gauges start off at about $25 for an app and you use your smart phone. If you want a permanently mounted solution, a scan gauge or ultra gauge is the better option.
It is quite surprising and interesting to see how the temperatures go up and down, and under what circumstances. Obviously working your vehicle hard means high temperature, but also in stop start traffic, or when its high ambient temperatures you’ll see them skyrocket.
What makes heat in an automatic box?
The majority of heat in an automatic transmission comes from the torque converter slipping. When its unlocked, you get a lot of churning of the Automatic Transmission Fluid (ATF) and this creates a heap of heat.
Different gearboxes work in different ways, but our Dmax will lock the torque converter up in 3rd, 4th and 5th gears. If you are working the vehicle very hard in first or second gear, the transmission gets super hot, super fast.
Unfortunately, there are cases where you have no choice but to be in first or second, so you just cop the excess heat! One of the highest temperatures we’ve seen in our Dmax was driving up the 5 rivers look out in Wyndham, where you couldn’t get above 40km/h and its a very, very steep hill. With the torque converter unlocked the whole way, we hit 107 degrees by the very top.
What can you do to reduce the heat?
If you want to keep the gearbox cooler, there are a few things you can do from a driving perspective. The first, is to aim for sitting in a gear that is locked up. In most cases, you can hear it lock up, and the revs will drop marginally (but no gear change happens) as the torque converter locks up.
Beyond that, the less work you make it do, the cooler it will be. The temperature difference between 100kmh and 110kmh in our Dmax is substantial, and this is reflected in fuel savings too.
It’s important to remember that you have low range too, which should be used when you are doing slow 4WD tracks and are working the vehicle hard. If we drive our Dmax in high range on the beach the temperatures get much hotter than in low range for the same speed.
Coolant cooling system check
Many 4WD’s with automatic transmissions have the cooling done at the bottom of your radiator. The automatic transmission fluid exits the transmission very hot, runs through the bottom of the radiator to cool it down and then returns.
What this means is that the cooling system for your motor is intrinsically linked to the cooling of your transmission. The hotter your coolant, the less ability it has to cool the transmission fluid, and the hotter it remains.
If your cooling system is not working perfectly (like when your viscous hub stops doing its thing) then you will notice an increase in your automatic transmission temperatures.
On another note, have a look to see if there is an external oil cooler for the automatic transmission already, as some do, and they mount them underneath the vehicle where they get nicely caked with mud, and then basically stop working.
Gear selection is another important note here, especially when towing. Some vehicles are not very intelligent with gear selection, and will happily labour the vehicle in 5th when it would sing along much happier in 4th. This is very vehicle dependant, but in many cases, 4th will result in lower temperatures.
Also, be aware that the top gears (5th onwards) in many gearboxes are overdrive, and not very strong. Extensive towing in the overdrive gears will often result in failure over time, especially if you are towing a significant amount of weight (2.5 tonne plus for a normal 4WD).
If you want to go down the path of reducing the temperatures even further, a transmission cooler is a very sensible option. Good quality units can be purchased for around $120 – $350, with complete kits for your vehicle often selling for around $500.
These are basically a small radiator that the transmission fluid goes through before going back to the transmission, and gives it much more surface area, and also a greater quantity of oil which helps dramatically in the cooling process.
Some 4WD’s come with external coolers from the factory, and many do not. The way to tell if you need one or not is to monitor the transmission temperatures under your normal use, and go from there. Everyone uses their 4WD differently, and not everyone needs one. For more information on this, check out this post; Transmission Cooler.
Lock up kits
There are a number of automatic lock up kits sold today for different 4WD’s, and they force your vehicle’s automatic transmission to lock up the torque converter at the flick of a switch. This provides you with proper engine braking, reduces the load on your brakes when descending and can substantially improve fuel economy and reduce heat in the transmission.
Automatic gearbox upgrades
Like most things on a vehicle, your automatic transmission can have upgrades installed to cope with more power, torque and pressure. Valve body upgrades are common, and these will help with longevity for vehicles that are working hard. Speak to a quality automatic transmission specialist for more information on this.
What’s the maximum heat?
Now, this is where things get interesting. I did a fair bit of reading online, and most of it suggests anything over about 90 degrees Celsius is bad for the oil, and even worse for your transmission.
Ideally, you don’t want your transmission fluid going above 100-110 degrees on a regular basis. At the end of the day, the hotter the fluid, the quicker it deteriorates and the harder life your transmission has. The warmer the automatic transmission fluid, the faster it loses its lubrication and drive properties and it will change from a red colour to a brown, and eventually black.
To care for your transmission you can run better quality oil, keep it cooler or change the fluid more often.
If you are regularly seeing temperatures above 100 – 110 degrees, I’d consider fitting a transmission cooler. The normal transmission temperature when towing something big in hilly conditions can be well over 100 degrees, and that’s not a good place to be.
Automatic Transmission Service
I’m sure that some manufacturers want your vehicle to fail at a certain point in time so they can make money repairing it. Some 4WD’s state that they have automatic transmission fluid designed to last the life of your vehicle.
This is an absolute load of crock. Anyone with any understanding of oils will tell you that it should be replaced at regular intervals. You only have to look at the colour change that takes place and it becomes very obvious.
The Dmax automatic transmission service interval is every 85,000km under normal operating conditions. If you are towing, they recommend doing it every 40,000km. If you have access to some of the oil, you’ll see the colour change as the oil loses its ability to work properly. If you leave it too long, you are at real risk of seriously expensive repairs.
The cost to flush the oil shouldn’t be more than about $500, and doing it every couple of years if you are working it hard will pay for itself in the long run. I had mine done at 40,000km and the oil was brown, but still good. My Dad had his done at 55,000km (Mitsubishi Pajero) with no aftermarket cooler, and the oil was black.
If it gets to this stage, you’ve likely shortened the life of your transmission as the oil loses its ability to do its job properly.
Take care of your automatic gearboxes
Automatic gearboxes are a thing of beauty; they really are. When they work, they are amazing, and a lot of people love them. However, if they stop working, they can be a hugely expensive and inconvenient thing to repair. Do the intelligent preventative maintenance, watch the temperatures and your automatic gearbox will reward you with years of good service.