Best Transmission Coolers: How to Choose the Right Transmission Cooler (2024)

It’s no secret that heat kills automatic transmissions.

This is especially true in big-power, street-strip machinesthat combine lots of horsepowerwith a small torque converter and steep rear axle ratio. Enginerpm is up across the board, and the automatic transmission builds heat. This is also true for trucksthat haul heavy loadsor tow trailers battling tough conditions such as long grades, high altitudes, or desert heat. In any case, loads coupled with stop-and-go traffic increase the heat level in an automatic transmission.

How Hot is Too Hot?

The ideal operating temperature for automatic transmission fluid is somewhere between 175 and 225degrees F. Here’s what can happen above this range:

  • At approximately 240degrees F, important additives begin to cook in the automatic transmission fluid (ATF). The result is the formation of varnish inside the transmission.
  • At approximately 260degrees F, 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 295degrees F, transmission clutch plates begin to slip because the oil is breaking down further.
  • At approximately 315degrees F, seals and clutches effectively burn out. Carbon forms in the oil and for all intents and purposes, the transmission is now junk. Often, a transmission will die within a few thousand miles (or sooner) if subjected to 300-plus degreeheat.

The built-in coolers that residein the bottom of the radiator are marginal at best. A typical “in-the-rad” cooler will reduce the heat of the ATF but it’s also influenced by the engine coolant temperature. And at the same time, it too can influence the engine coolant temperature.

How can that happen?

If the vehicle in question has a thermostat that opens at 195degrees F, once warmed to operating temperature, the transmission cooler will have a tough time reducing the heat of the ATF below 195degrees F. At the same time, if the transmission is overworked, it might raise the operating temperature of the ATF to 250degrees F or more. This heatcan be transferred to the engine coolantresulting in a potential boil over.

So what’s the answer?

You can add an external cooler. But before you rush out and buy the first cooler available, here’s an example to ponder:

Decades ago, webuilt an L88 powered 1969 Camaro complete with a turbo 400, a 12-bolt filled with 4.88:1 gears and an 8-inch torque converter. It was a street-driven car, but even with a big, four-core rad, the combination was always ready to melt the transmission fluid. In a conversation with Bob Fouts at Earl’s Performance, we garnered this critical kernel of information: Itis virtually impossible to overcool an automatic transmission, especially one in a high performance application. Naturally, this might not apply to vehicles operating near the Arctic Circle, but in the rest of the world, it basically holds true.

Types of Coolers

Typically, there are two types of cooler styles available: “tube-and-fin” and the “stacked plate” cooler. A conventional tube-and-fin cooler is the most common type you’ll find. Generally speaking, this cooler configuration consists of fins that are placed over aluminum tubes, which are laid out in “S” patterns. The idea is to have air flow over the fins, which in turn creates a heat sink effect. This effect draws heat from the ATF. Tube-and-fin coolers are inexpensive and easy-to-build.

The other type of cooler that is available is the “stacked plate” design. This cooler is laid out in much the same manner as the radiator in your car. Rather than using a tube to carry the ATF inside the cooler, the fins actually form the passage for the fluid to pass through. This is almost identical to the process Detroit uses to build modern radiators. This type of cooler configuration is much more efficient than the tube-and-fin style. And if you search the Summit Racing website, you’ll see all sorts of good options, including top-of-the line versions from Earl’s Performance.

The stacked plate, or “modular” cooler, has been in use since prior to WWII. During the early 1930s, it was first developed for use with the Rolls Royce Merlin engine that powered the Spitfires and Hurricanes in the Battle of Britain. It was ideal because of its dense air fins and “turbulator plates” which provide maximum liquid side (internal) and airside (external) surface area. The collector or end tanks ensure minimum flow restriction, while the fully brazed construction results in the most efficient possible thermal transfer between liquid and air. Thisold Rolls Royce Merlin design is the most thermally efficient liquid-to-air heat exchanger format available.

Now, you’re probably saying: “there’s a big difference between the conditions seen in an aircraft and those experienced by my street driven car.” That’s true, but these old war birds were subsonic and piston powered. In today’s terms, those old aircraft were dead slow, and because of that, heat exchanger technology has more in common with today’s trucks and cars than you might think. Plus, a heat exchanger or cooler doesn’t know if it’s cooling engine oil, hydraulic fluid, or ATF. When this basic, modular design is utilized, and the oil flow and air speed of the vehicle is taken into consideration, then the optimum heat exchanger can be produced.

Stacked Plate vs. Tube-and-Fin Coolers

How effective is the stacked plate, modular design in comparison to a more common tube-and-fin arrangement? Typically, a modular cooler (such as the Earl’s coolers shown in the photos below) will reject as much as three times the heat for a given area than a tube-and-fin cooler. The modular configuration cooler will also have less than half of the pressure drop found in a tube-and-fin cooler.

Copper-Bass vs. Aluminum Coolers

When it comes to heat exchanger construction, what’s best: copper and brass or aluminum? In most cases, the aluminum exchangers are nearly as thermally efficient as the copper and brass versions, but significantly lighter. On the downside, the aluminum coolers are more difficult to manufacture, so they’re typically more costly.

Another thing to consider is the paint. The common black paint that is preferred by most local radiator shops can act as thermal barrier instead of promoting the transfer of heat. A proper aluminum heat exchanger will either be anodized, or it will have a very thin coat of baked, heat exchanger paint (typically grey, silver, or black in color).

FluidCooler Mounting Tips

According to Earl’s Performance Products, the cooler must be mounted in a stream of moving air at ambient temperature to operate efficiently. It is not a good idea to mount the oil cooler behind the radiator where it will receive only heated air. It is not enough to lead air to the cooler; the heated air must have somewhere to go after it passes through the core. Air naturally flowsfrom a region of relatively high pressure to a region of relatively low pressure, so you should mount your cooler in the airstream ahead of the vehicle radiator. That way, it will always be subject to high pressure at the face, and the engine fan will always provide a region of low pressure behind the cooler.

You also need to consider the location of the inlet and outlet ports. Coolers should never be mounted so that both the inlet and outlet ports are on the bottom. The best method is to have the ports on the top. If this isn’t possible, the next best scenario has the cooler mounted on the side so that the ports are arranged horizontally.

There are a number of ways to mount the cooler; however, Earl’s offers a slick system for their coolers. This aluminumbracket is designed to hold the cooler securely without damage from vibration. Included is a pair of brackets (with integral rubber cushions) and e-coated aircraft quality hardware with rubber insulators spacers. Earl’s offers this bracket system for all of their Temp-A-Cure cooler models.

Port configuration is usually a matter of preference. The Earl’s coolers incorporate -10 AN O-ring boss ports. From here, you simply select the AN adapter that suits your needs. It’s no secret AN fittings are less prone to leakage and obviously much more secure than pipe thread examples. A-6 AN arrangement is most commonfor an automatic transmission.

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When it comes to automatic transmission coolers, bigger is always better. This cooler measures 8-1/4 X 13-inches (Earl’s #24200ERL). It's big but as indicated in the text, it's impossible to overcool an automatic transmission. Earl's offers coolers in a wide range of configurations.

Even larger is this Earl’s cooler. It measures 8-1/4 X 18.5-inches in size (Earl’s #26000ERL).

When mounting your cooler, keep in mind that heat exchanger (like engine radiators) do not work well if the liquid side is filled with air. Coolers should never be mounted so that both the inlet and outlet ports are on the bottom. The best method is to have the ports on the top. If this isn't possible, the next best scenario has the cooler mounted on the side so that the ports are arranged horizontally.

Earl’s coolers are manufactured with -10 AN female O-ring ports. From here, you simply use an AN adapter to go to your cooler hose size (which is typically -6AN – Earl’s #585106ERL shown here).

Up close, you can see the "modular" construction format. This type of cooler features dense air fins and "tubulator plates" that provide maximum liquid side (internal) and air-side (external) surface area. The collector or end tanks ensure minimum flow restriction, while the fully brazed construction results in the most efficient possible thermal transfer bath between liquid and air.

Although there are a number of ways to mount the cooler, one of the best that we've seen is the cushioned aluminum mount arrangement used by Earl's (Earl’s #1302ERL for the narrow coolers shown in the article). Manufactured from aluminum, this bracket is designed to hold the cooler securely without damage from vibration. Included is a pair of brackets (with integral rubber cushions) and e-coated aircraft quality hardware with rubber insulators.

The backside of the aluminum mounts (extrusions) is permanently fitted with rubber cushions. These cushions protect the heat exchanger from unwanted vibrations. Both the top and bottom mount brackets include this cushion arrangement.

This is how the mounting arrangement looks assembled on the cooler. It’s stout, secure and light.

Selecting a Cooler Size

Forhigh performance street cars or trucks that aresubjected to heavy loadsor towing,bigger is always better. As we’ve already mentioned, it’s impossible to overcool an automatic transmission.

The nature of the Earl’s Temp-A-Cure cooler (shown in the slideshow) allows it to be manufactured in countless different sizes. In fact, Earl’s offers a wide array of coolers to suit almost any application. The narrow 8¼-inch wide coolers are available in heights ranging from 2 to 18½ inches. Along with the narrow coolers, you can purchase wide body coolers. The “extra wide” coolers from Earl’s have a width of 15¼ inches and heights range from 2 to 18½-inches. Finally, Earl’s manufactures curved coolers that have a width of 11.562-inches and a height from 3.05 inches up to 4.919 inches. Basically, any cooler with a face height up to 18½ inches can be created.

In the end, money that’s spent on a proper cooler is like money in the bank. Not only will your transmission live longer, it will also be more efficient.

Best Transmission Coolers: How to Choose the Right Transmission Cooler (2024)

FAQs

How to choose the right transmission cooler? ›

Choosing the right size of transmission cooler is important to ensure that it can handle the amount of heat generated by your transmission. The general rule of thumb is to choose a cooler that is rated for at least three times the weight of your vehicle or the weight of the trailer you are towing.

What is a good transmission cooler? ›

A stacked plate cooler or a plate and fin cooler is ideal for these transmissions, as they offer the best performance and durability. Additionally, installing the cooler in front of the radiator or the grille area is recommended to ensure adequate airflow.

What does a bigger transmission cooler do? ›

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.

Can a transmission cooler cool too much? ›

Not if you install it properly. If you put the transmission fluid cooler in series with the OEM intercooler in the radiator, with fluid going through the intercooler last, then over-cooled transmission fluid should be warmed back to operating temperature before going back to the transmission.

How do I choose the right cooling system? ›

Choose the right cooling system by considering which type of process fluid cooling system is best for your application. In this process it is important to determine the process fluid medium, desired temperature, and the significance of operating cost versus initial investment.

Should I put a fan on my transmission cooler? ›

Well, it turns out that a good plate style cooler and small electric fan will cool a transmission like none other, and can be mounted underneath the car. Yep, and it loves it.

Will a transmission cooler make the transmission last longer? ›

Increases Transmission Life Span

In such situations, adding a cooler will drop the temperature by 20 to 25 degrees, maintaining your transmission temperature in the 170F range. At this temperature, your transmission could last upwards of 100,000 miles.

Can I run two transmission coolers together? ›

It is definitely possible to run two transmission coolers together. Having an auxiliary cooler is an excellent way to improve the overall cooling of your transmission. The factory cooling is not always adequate for the tasks we demand of our vehicles. This is a reason to fit an auxiliary cooler.

Are bigger coolers better? ›

Insulation and Ice Retention

Remember that larger coolers generally have better ice retention due to their higher insulation-to-surface-area ratio. You can also fit more ice in a larger cooler, to begin with.

Can you overcool an automatic transmission? ›

Transmission oil coolers and how cool should you go.

Here's a link to the etrailer transmission oil cooler FAQ that says, except in extreme cold climates you cannot over-cool your transmission. And, even then it just requires a couple of minutes of warm up time before driving.

What is considered too hot for transmission? ›

The optimal temperature range for transmission fluid is 175 to 220 degrees. Above that, for every 20 degrees, bad things happen, starting with the formation of varnish at 240 degrees, followed by seals hardening, plates slipping, seals and clutches burning out, carbon being formed, and, ultimately, failure.

Should I flush my transmission cooler? ›

Without cleaning the transmission cooler, you shouldn't even waste time flushing the transmission. The dirt and contaminants in the cooler will simply work their way back into the transmission, neutralizing any benefit your flush may have provided.

Are transmission coolers standard? ›

In almost all vehicles with an automatic transmission there is a transmission cooler placed inside the radiator. Most standard transmissions do not make as much heat and therefore do not have a cooler.

Does adding a transmission cooler really help? ›

Keeping Your Cool

In terms of transmission operating temperatures keeping the fluid 200 degrees or less is preferred for long life — for every 20-degree increase in temperature above that, the life of the fluid is cut in half.

Which transmission cooler line is which? ›

Bottom is the drain line, or too the radiator. Top is fill, or from the radiator. If you put them in the other way around, the top line most likely will not pull fluid out to the radiator.

Does a transmission cooler make a difference? ›

These types of coolers have been around as long as the automatic transmission and for the most part do an effective job of keeping the transmission going for many thousands of miles. The in-the-tank coolers not only perform the job of cooling the fluid, but warm the fluid in extremely cold environments as well.

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