• Marshall

Is a larger transmission cooler enough?

We don't often get the chance to look into the performance of various products, however during the development of auto-mate for the 4 speed Triton we had access to a vehicle which already had a larger after-market transmission cooler installed, yet still had a problem with the transmission overheating and going into LIMP mode.

The performance results were very surprising

The customer was considering installing another transmission cooler, but instead he joined our Triton (4 speed) pre-release test program and purchased a lockup kit (auto-mate). He was soon to take delivery of a 2.5t (tare) caravan and needed to solve the problem.

What are the key differences?

Transmission coolers and lockup kits have completely different philosophies to keep the oil cooler:

remove the heat vs stop the heat
Typical larger after-market transmission cooler

An upgraded transmission cooler (or radiator if you wish) is larger than the factory cooler and can remove more heat from the transmission oil. Often they are also accompanied by an external fan.

A larger transmission cooler certainly extracts more heat, but unfortunately it's usually located in front of the air conditioning and engine radiator. As a result, this hotter air reduces their cooling performance.

Torque Converter

The lockup kit is different. It targets the root cause of heat which is the torque converter. By locking the torque converter clutch it eliminates slipping which under high loads is the major heat source. With a lockup kit installed you don't need to upgrade the factory transmission cooler.

The goal is to keep the transmission temperature within the ideal range of 60-80 degrees.

Test Vehicle

For this test we borrowed a nicely modified 2015 Triton MN with the 4 speed auto. We were using this vehicle for pre-release testing for this auto-mate model.

Modifications include an ECU remap, transmission cooler upgrade, intercooler upgrade, 3" exhaust, 32" tyres, 2" suspension lift, REDARC boost and EGT gauge, plus all the expected fruit in a touring 4WD (bull bar, winch, canopy, roof racks, snorkel, spotlights lights, drawers, fridge etc).

This is a seriously nice setup!

The Test Route

We wanted to keep the test as 'real-world' as possible. We decided on a test route through the Adelaide Hills which was not too onerous on the transmission.

The vehicle was unloaded as used for daily driving, and was not towing anything.

This was a typical country touring route with a mix of winding roads and straights with speeds ranging between 40 to 80 kph and one steep 3 minute climb. On this route the factory ECU would rarely lockup the torque converter, so it provided a great comparison of the performance difference using a lockup kit and an after-market transmission cooler to manage transmission temperature.

The route would be driven twice in a similar manner with both auto-mate ON (the auto-mate run) and OFF (transmission cooler only run). For both runs the transmission was in DRIVE.

The route distance was 45km return and took 49 minutes to complete (pretty close to the 50 minutes predicted on the map below). We completed each run within 30 seconds of each other. The average speed on each run was the same at 55kph. So the results are an apples for apples comparison.

After 3 minutes from the start of the route in city traffic it was an 80 zone most of the way with no stops or traffic lights. Traffic was light and thankfully there were no holdups behind slow vehicles, ie, a clean equivalent comparison. On the map we drove clockwise to the point marked 671 Paracombe Road, then turned around and drove anti-clockwise back to the start. Hence a mirror reverse of the route and a net 0m elevation change.

The Results

Our data logger was attached to the vehicle to measure a variety of parameters including time, speed, rpm, gear and the transmission pan temperature. The pan temperature sensor is internal to the transmission and measures the temperature of the main oil reservoir (the pan). The temperature at the output of the torque converter would be 10-20 degrees higher than the pan temp. The temperature was obtained via the CANBus from the transmission ECU and logged.

Now for the interesting bit - we didn't know the results until the data was downloaded for analysis.


I must admit these results were unexpected as I thought a larger oil cooler would have performed better, but it explains why this vehicle still had a transmission temperature issue. Each way the temperature difference was compared (peak maximum minus minimum or using the averages), auto-mate was 25 deg C cooler. The peak 101 deg C pan temperature was with auto-mate OFF and was after the steep climb, so the oil temperature at the torque converter outlet would have been over 120 deg C during the climb. You can see the 3 minute steep climb in the middle of the graph.

The auto-mate run started at 72 deg C and the transmission cooler run (ie, auto-mate OFF) at 66. After 3 minutes we were out of the city limits and in fresh air of the 80 zone and going uphill. You can see the temperature of the auto-mate run stop rising and start to drop, and the transmission cooler run start to increase quickly during a long steady 70-80 kph uphill section.

During the first 15 minutes auto-mate actually cooled the oil down to 66 (-6 degrees). In contrast, with only the larger oil cooler it climbed to 98 deg C. That's a +32 degree increase!

There after it peaked at 101 deg C, whereas the auto-mate peaked at 75 (well within the ideal temperature range).

At the start we said the ideal transmission temperature is between 60 to 80. Once you're reaching 100 you should start to be concerned and at around 120 take action (like stopping) .

The final 10 minutes was the same section of road as the first 10 minutes but downhill. In the data you can see both cooling down.

At the finish line, auto-mate 65 and transmission cooler 95 (30 deg C more and we were not towing)

This was surprising as we had assumed the oil cooler would perform well. Regardless, you can see why the transmission was overheating, and that auto-mate has solved the customer's problem.

Without further investigation we couldn't conclude why it was so hot even with the larger cooler. However, in this vehicle there are restrictions to airflow caused by the spotlights, winch and bullbar. Also, the engine ECU remap would generate more heat, and the front mounted intercooler would be pushing hotter air into the transmission cooler, which in turn put this air into the radiator. So there are a number of factors which could be explored.

In our previous testing we've seen the lockup kits also reduce engine coolant, air intake and EGT temperatures. Basically the engine doesn't need to work as hard, so you're rewarded with lower overall temperatures and fuel savings.

The customer reported that on a long hill he travels up regularly at 100 kph he'd see high exhaust gas temperature (EGT) and the alarm (set at 650) would activate.

With auto-mate, up the same hill at 100kph, the EGTs dropped from above 650 to 500 deg C (~25% less) as the engine didn't work as hard.

Same Test in the Pajero (NX 2016)

Because of these surprising results we wanted to investigate further. Several days later we repeated the same test using our NX Pajero which has a standard transmission cooler, similar front setup with bullbar, winch, snorkel, and spot lights (but only two). No engine ECU remap or upgraded intercooler or transmission cooler - so 'stock'.

The results from the Pajero runs were as expected given the car was unloaded and not towing. They showed that with auto-mate OFF the stock transmission cooler performed well and kept the pan oil temperature within the 60-80 degree range (the torque converter oil peaked at 94 degC).

With auto-mate ON, it averaged 8 deg C cooler at 68 which over time would extend the oil life.

In the first 5 minutes up the hill, auto-mate actually cooled the oil (-4 deg C), whereas otherwise it increased by +13 deg C.

Also of interest is the oil temperature at the finish of the auto-mate ON run was 11 degrees cooler than at the start.

The ON run started after the OFF run, hence the higher starting temperature.


The key conclusion from our tests demonstrated that even though you may have installed a larger transmission cooler, it may not be performing adequately and may not be enough. This is especially true if you've modified the engine's performance. My advice, as always, is to monitor your temperatures.

auto-mate, however, reliably reduced the transmission temperature (25-30 deg C lower). With an auto-mate installed you don't need to upgrade the stock transmission cooler.

So, if you want to reliably protect your transmission from high temperatures and avoid LIMP problems (and save fuel in the process) get one of our lockup kits which are the most sophisticated available. Head to the web-site for more details.

Safe travels,

Marshall and the MM4X4 team


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