Frequently Asked Questions About Transmission Coolers

Because your automatic transimssion works harder when you tow, it can get hotter, and heat is one of the major enemies of your transmission. An aftermarket transmission cooler can keep your transmission from getting too hot, helping you get the best performance and long life out of it. If you are considering a transmission cooler, you may have questions. If so, we have some answers. Check out the questions, below, to find out more about transmission coolers.
Transmission Cooler Diagram

1. How does a transmission cooler function?

Fluid heated by the transmission, engine, or power steering pump flows to the cooler. The air moving over the fins of the cooler cools the fluid, which is then routed back to the transmission, engine or power steering pump in a continuous loop through the return line.

2. How do you attach the transmission cooler in front of the radiator or air conditioning condensor?

Several different options for mounting a transmission cooler are available. In the most common installation method, the cooler is attached with narrow plastic rods, pads, and fasteners. The plastic rods are run through the transmission cooler and the radiator or air conditioning condensor and secured with the fastener. Another option is to use a rigid mount kit that includes bendable brackets to mount the cooler. You can use this option if the cooler has mounting points designed for brackets and your vehicle has suitable mounting points. A third option that consists of solid mounting brackets is available for stacked-plate type coolers. Click here to see available mounting kits for transmission and engine coolers.

3. What is the difference between the tube-and-fin cooler, the plate-and-fin cooler and the stacked-plate cooler?

The main difference is in the ability to cool the fluid. The tube-and-fin style has a tube that carries the transmission fluid through the cooler. It is also distinguished by its turbulators, which agitate the fluid to get more of it to contact the aluminum in the tube. Aluminum fins are attached to the outside of the tube and, since aluminum dissipates heat quickly, the heat from the fluid is absorbed by the aluminum, moves out to the fins, and is then carried away from the cooler by the air flowing through the fins on the outside of the cooler. This style of cooler works well but is the least efficient type of cooler that we carry.Plate-and-fin coolers work on the same principle as the tube-and-fin-style coolers but are more efficient. Plate-and-fin coolers force fluid through much smaller plates that, like the tube-and-fin cooler, cause turbulation (or agitation) of the fluid. But fluid in the plate-and-fin style is cooled better before leaving the cooler because the smaller, flatter plates allow more fluid to contact the aluminum surface inside the cooler. Stacked-plate coolers are the most efficient coolers. They have the same design as the plate-and-fin style, but they have high-flow turbulators for heavy-duty towing or race applications. The stacked-plate design uses AN (Army-Navy) fittings, which are popular in high-performance and racing applications where the cooler may need to be installed and removed more frequently than in a typical towing setup.
Tube and Fin Style Transmission Cooler
Plate and Fin Style Transmission Cooler
Stack and Fin Style Transmission Cooler

4. If there are 3 coolers all listed for the same weight, how do you know which one is best?

The first consideration would be the size of the cooler. Generally speaking, the larger the cooler, the better the cooling performance will be. If there are similarly sized tube-and-fin coolers and plate-and-fin coolers, then the plate-and-fin cooler will perform better even if it is slightly smaller. The second consideration is the mounting location. If you mount the transmission cooler behind the radiator or between the radiator and air conditioning condenser, a more efficient cooler is required to provide the most efficient cooling.
Best Transmission Cooler Location

5. Why are coolers rated by Class?

Because we are in the towing industry, our customers are used to seeing Class ratings on their trailer hitches, so this is an easy way to alert the customer as to which cooler is the most efficient for their towing needs. Therefore we use the Class rating to let customers know that if they have a Class II hitch on their vehicle, then a Class II cooler should be sufficient, but they can always use a larger cooler for more cooling if they like.

6. Shouldn't I get the one rated for the highest weight capacity? Why or why not?

The general rule is that transmission fluid cannot be cooled too much, so using the largest cooler that will fit is a good idea, especially if you are towing. The only reason not to add the largest cooler possible would be if you live in a very cold climate where temperatures are commonly below 0 degrees and you have a transmission cooler installed. This would warrant warming the engine for a few minutes. Most people warm the engine in these cold conditions anyway, so size is not a factor.

7. Will this mess up my factory transmission?

No. As long as it is properly installed, a transmission cooler will not affect a factory transmission. It is a flow-through device and does not affect any internal components of the transmission. A transmission cooler will just help to prolong the life of the transmission by keeping the fluid cooler. Transmission fluid cannot be cooled too much, so the addition of a cooler is a good idea, especially if you are towing.

8. Does the transmission cooler do anything if you are not towing?

Yes. The transmission cooler is a flow-through device and operates anytime the engine is running. The fluid will flow from the transmission to the OEM cooler and then to the aftermarket cooler; and finally, the cooled fluid flows back to the transmission in a continuous loop.

9. If the transmission cooler is a custom fit why do I need to measure?

The cooler itself is not the custom-fit part. We have transmission coolers in the fitguide because some vehicles, mostly GM, Ford and Chrysler/Dodge, can use custom fittings to make installation of the transmission cooler easier and faster.
Transmission Cooler Installation Diagram

10. Are custom fittings available for most vehicles?

No. For most vehicles you will use an Insta-dapt fitting that is included with the transmission cooler and that connects directly to the OEM transmission cooler. Then the rubber hose going to the aftermarket transmission cooler is clamped to the fitting, and the hose coming from it is slipped over the original line and clamped. Or, the Insta-dapt is installed in-line between an OEM hose and the transmission cooler hose. In addition, some vehicles will require that you cut and flare the OEM steel or aluminum transmission return line and then clamp the transmission cooler hoses directly to the two ends of the cut line. Note: Many installers prefer this type of installation because they already have the cutting and flaring tools and no extra fittings are needed.

11. How do I install a transmission cooler when special fittings are available?

Special fittings are designed to make it easier and faster to install a transmission cooler. Most vehicles for which fittings are available have either snap-in fittings or threaded flare fittings that can be used to connect the rubber hoses going to and coming from the aftermarket transmission cooler in-line with the transmission's return line and the OEM transmission cooler.

12. How do you know if you need special fittings?

Our year-make-model fitguide will list the special fittings needed for a specific vehicle if they are available from our supplier. This is why transmission coolers are listed in the fitguide on our website.

13. What is a hose barb?

A hose barb is the part of a fitting that the rubber hose slides over. The hose is then secured with a hose clamp. Often the transmission cooler will have hose barb fittings for connecting the rubber hoses to it. Click here to shop for radiator adapters.
Transmission Cooler Hose Barb Fitting

14. What does NPT mean?

NPT stands for National Pipe Thread, which is a standard for threaded fittings in the plumbing industry. Much like AN (Army-Navy) fitting, it is a way of identifying the type and size of fittings needed for an installation application.
NPT Fitting
AN Army/Navy Fitting

15. Can all coolers be used on any vehicle out there or are the ones listed in the fit guide search only for that year, make and model?

A transmission cooler is a flow-through device and is not designed specifically for any particular year, make and model. Any cooler can be used on any vehicle with an automatic transmission, provided that it will fit in the location where the customer wants to install it. Year-make-model fittings are available for some vehicles to make it easier to install the coolers. You can use the fitguide to determine whether a vehicle can use a custom fitting.

16. Just because the fitguide does not list a transmission cooler for a vehicle can someone still put one on?

Yes. The installer will need to determine how to install the cooler on the vehicle. Any of the installation procedures explained previously can be used. We do not list a transmission cooler if we do not have information from the transmission cooler manufacturer or when the vehicle manufacturer does not recommend installing a transmission cooler on the vehicle.

17. Can I use an oil cooler, power steering cooler and transmission cooler all together?

Yes. You can install all three on the vehicle. You would need three separate coolers and have the space needed to install each one. We carry some dual-function coolers. These are basically two separate coolers in one with an inlet and outlet for two different fluids. Click here to see available dual-function coolers.
Combination Cooler

18. Do the coolers mount in the same location as other items, like power steering coolers and engine oil coolers?

Yes. If you are installing more than one cooler you will need to carefully consider the fit. As long as there is enough room, it is possible to install all three coolers.
Best Transmission Cooler Locations

19. I have lines running from my transmission to my radiator. How does the transmission cooler actually install to the radiator?

Transmission coolers do not attach to the radiator. They attach in-line with the transmission fluid return line. It is common for an OEM transmission cooler to be built into the radiator tank to be cooled by the coolant in the radiator.

20. Does the transmission cooler need to be installed with the hose fitting in any certain position?

No. The cooler can be installed with the hose fittings in any position that will make the installation easier or look more professional on the vehicle. It does not matter which fitting on the cooler is used for the inlet or outlet.

21. Do I need an oil cooler also?

Oil coolers are optional. Many people choose an oil cooler when their towing application is heavy duty, such as towing a fifth-wheel trailer or gooseneck trailer. The oil cooler is based on the same flow-through principle as the transmission cooler. It is installed in-line with the vehicle's oil delivery system, and then the oil pump pushes oil through the cooler and back into the engine. If a vehicle manufacturer recommends an oil cooler for towing, then it would be needed for that vehicle. The customer should check the vehicle owner's manual.
Updated: 3/2/2021

Questions and Comments about this Article

Robert J.

I have a 2021 Toyota Sienna Hybrid van, can a transmission cooler be put on it. It had the ecvt transmission in it Thanks

Etrailer Expert
Reply from Victoria B.

@RobertJ It may be possible for an auxiliary cooler to be installed on your van, but it would likely not be as simple as an installation on a traditional system. I believe that most if not all CVT systems are closed, so there is nowhere to check the transmission fluid level or add more if needed. This can make adding more fluid to the system after an aux cooler has been installed more difficult and most time is best done by a professional.


Which the gap (spacing) between trans cooler and a/c condenser or radiator?

Etrailer Expert
Reply from Victoria B.

@Ricardo there is no standard for how close or far away the auxiliary transmission cooler needs to be away from the radiator. In most installations the auxiliary cooler ends up installed right next the the radiator with only thin foam pads for separation. You will want to make sure the cooler does not get in the way of any moving parts, such as the fan, and still has airflow to cool the fluid.


My truck(2003 Silverado) has a transmission cooler installed on it,—-now I’m installing another radiator & I have a small rubber hose left over w/no place to connect it. Should I just plug it off ? .

Felix R.

Can you use a transmission cooler as an aux radiator for coolant

Etrailer Expert
Reply from Victoria B.

Yes! This is exactly what an auxiliary transmission cooler is designed to do.

Matt S.

Do I need to add more fluid to the transmission after adding a cooler? If so, how much?

Etrailer Expert
Reply from Victoria B.

@MattS As long as your vehicle does not have a closed system, there will be a dipstick under the hood to check the transmission fluid level. After you install an auxiliary cooler into the system you will want to check the dipstick to see if the fluid level is low and add more based on how low the dipstick reads.

Dawson M.

Does the cooler need to sit right against the condenser, or can there be a gap in between the cooler and condenser? I figure it could create turbulence and reduce the cooling potential of the radiator

Etrailer Expert
Reply from Jon G.

It doesn't necessarily HAVE to sit right up against the condenser - it just tends to work out better that way due to space and having a stable installation. If you're able to have it sit out a little further and you have a way to keep it stable while you're heading down the road then go for it.


Is the stock 5 X 9" transmission cooler on 2003 GMG sierra 1500 Z71 good enough for pulling a 6k trailer?

Josh S.

Does a transmission cooler set up need to sit at at certain level relative to the transmission? Can the entire radiator sit higher than the transmission? would that require an electric pump somewhere in line?

Etrailer Expert
Reply from Jon G.

There are no specific mounting heights that are required when installing a transmission cooler. Your transmission will already have the means necessary to allow the fluid to run through it. The aux cooler (like what we have) will just give you more capacity and real estate to cool the fluid so no electric pump is required.

Dennis C.

My question, will any of these coolers handle the transmission as a stand alone? I don't want to use the OEM radiator for cooling my tranny? and is there a kit to connect the cooler this way? I'm \also looking to add a Temperature and pressure , do you have kits?

Etrailer Expert
Reply from Jon G.

We do not recommend using one of our transmission coolers as a stand-alone cooler. These are designed to supplement your OEM cooler and shouldn't be used individually. Are you asking about a temperature and pressure gauge or something else? We do have some tuners and monitors that you can check out through our fitguide. These can be used to give you more detailed specs about your vehicle.


I am using a 2015 gmc terrain. towing a 4 x8 u haul trailer . Only a few hundred pounds of weight inside the trailer. Going about 800 Miles 1 time only. I am the only passenger. Do I still need a transmission cooler installed?

Etrailer Expert
Reply from Jon G.

I think you'll be okay. Just make sure that you have everything loaded correctly and that your cargo is adjusted so that your tongue weight doesn't exceed what your GMC Terrain is rated for.

Reply from Travis

@Joe Joe, with that little weight, you have nothing to worry about. You’re good to go.

Dave B.

How do I tell if my truck already has an add-on transmission cooler either aftermarket or from the factory? (2018 Nissan Titan SV)

Etrailer Expert
Reply from Jon G.

If the truck has 2 factory transmission coolers you can call your local dealer with your VIN and they should be able to tell you. If it's aftermarket then you should be able to see your send and return lines connected like what you see in the photos on this helpful page.

Reply from Dave B.

@JonG thanks! I'll check it out.

John S.

Class ratio ? Class I Class II or Class III, Class III is better cooling Then I

Jerry F.

what size are the fittings on the radiator for the transmission lines? 3/8 is to small, 1/2 is to big. Must be metric? 04 jeep grand cherokee limited 4.7 full time 4wd. Trying to install an auxillary tranny cooler but can not find any fittings that will fit the radiator and tranny line

Noel W.


Etrailer Expert
Reply from Kef G.

The best place to mount a transmission cooler is in front of the radiator. The space there will determine which size you should get. Unfortunately, that space isn't something that is documented, so you will need to measure the length, width, and depth available in that area to find what size would work for you.



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