Is an aftermarket transmission cooler required?

New car manufactures make a car to a price and ensure it meets the expectations of most customers. If you aren’t towing are are running standard power then, quite rightly, you probably won’t be thinking of adding a transmission cooler. If you want to be more scientific, then measure the transmission temperature and decide if you are comfortable with the temperatures you are seeing. If you will be towing a caravan or camper trailer then it is sensible to install an external transmission cooler, to make the transmission last as long as possible by keeping the temperatures down.

The ideal operating temperature for automatic transmission fluid is somewhere between 80 and 110 degrees C. Here’s what can happen above this range:

• At approximately 115 degrees C, important additives begin to cook in the automatic transmission fluid (ATF). The result is the formation of varnish inside the transmission.

• At approximately 125 degrees C, internal transmission seals, which are often manufactured from a polyacrylate material, begin to harden. The end results are internal and external leaks as the the seals lose their elasticity.

• At approximately 145 degrees C, transmission clutch plates begin to slip because the oil is breaking down further.

• At approximately 160 degrees C, seals and clutches effectively burn out. Carbon forms in the oil and your effectively killed the transmission. Often, a transmission will die within a few thousand km after experiencing 150-plus degree heat.

It is worth noting that the AT temp warning light on a 4 speed auto Landcruiser came on at 150degC and that generally means you are well beyond a safe temperature.

When adding an aftermarket transmission cooler, can you go too big?

In Australia with our high temps and the area available to mount transmission coolers the answer is no. The only reason for running a smaller unit is cost and this will mean a lesser capable unit.

Single piece steel brackets.

We use 3mm mild steel brackets which have been zinc plated and coated. Using one piece bracket to hold the cooler means flexing of the cooler is kept to a minimum and and body flex or vibration are much less likely to hurt it.

Stainless brackets look smart and don’t need a coating, but stainless steel will cause an anodic/cathode reaction resulting in corrosion in the cars body around where it is mounted since the exposed metal allows electron transfer, which is the start of the process.

Stacked Plate or Plate and Fin?

The market doesn’t seem to have tube and fin units, which were cheap (easy to make) and are the most inferior design. The next step up in efficiency and still cost effective are the “plate and fin” design. These seem to be the most commonly available units and come in a few different sizes. Dual setup versions of these are available to increase efficiency and the fluid has to run through both units. This means extra connections, double the restriction to flow and the resulting overall efficiency not equivalent to double the single unit.

Stacked plate design is the optimal setup being the most efficient and durable construction, which is why PDI use them. The internal restriction to flow is minimal, which is important as there is lots of flow through these units and restricting flow may affect the life of the transmission.

All PDI air to air intercoolers use a “bar and plate” design and are durable and highly effective in this application. We have seen a bar and plate system used as a transmission cooler, but when compared to a stack plate fluid/air cooler the bar and plate aren’t very effective. Our testing was with bar and plate cooler that was over six times the size of the stacked plate cooler.

In front of the intercooler or behind?

The intercooler has the potential to extract lots of heat. For example, the highly efficient PDI intercooler fitted to a Landcruiser 100 series when towing a heavy camper trailer at 100kph is able to drop the intake air temperatures down from 150-160deg to 40deg on a 25deg day. The heat removal can be much high when pushing hard along a beach. With this heat loading in front of a transmission cooler it can be hard to drop transmission temperatures when it is most required.

Transmission coolers aren’t always working - when the torque converter is “locked up” the transmission isn’t making anywhere near the heat it can do when the torque converter is working. Normally for highway driving the torque converter is locked up so there is no extra load being placed in front of the intercooler in this situation, however on the beach with the torque converter unlocked we want to give the transmission the best chance to not get too hot so prioritise transmission cooling.

We also don’t see the point in hiding the cooler behind the lower bumper where air flow is limited and we can’t be expected to see much heat extraction.