Shop All Transmission Parts →
An auxiliary transmission cooler only works when air is moving through it. At highway speed the cooler sees plenty of ram air and your temps stay flat. The problem is the slow, heat-soaked situations: crawling up a grade, sitting at a light with a loaded trailer, backing a boat down a ramp on a hot day. That is exactly when transmission temperature climbs, and exactly when there is no airflow. An electric fan on the cooler fixes it.
Two questions decide the fan you buy: how much air do you need to move, which is set by cooler size and how hard you tow, and pusher or puller, which is set by where you mounted the cooler. Get those two right and the wiring is the easy part.
Pusher vs Puller — The Decision Tree
Pusher Fan (Mounts in Front of the Cooler)
A pusher fan sits on the front face of the cooler and shoves air through it toward the engine bay. This is the usual setup for an auxiliary transmission cooler mounted ahead of the A/C condenser and radiator, because there is room in front and you are simply forcing air through a cooler that is already in the airstream. Pusher fans are slightly less efficient than pullers but for an add-on trans cooler they are the practical choice.
Buy a pusher if: your cooler is mounted in front of the condenser, or anywhere with clearance on the front face.
Puller Fan (Mounts Behind the Cooler)
A puller fan sits behind the cooler and draws air through it. Pullers move air more efficiently and do not block incoming ram air, but they need clearance behind the cooler, which an auxiliary trans cooler stacked in front of the condenser usually does not have.
Buy a puller if: the cooler is mounted where you have room behind it and nothing important in the way.
For the typical bolt-on transmission cooler zip-tied in front of the condenser, a slim pusher fan is the answer. Do not fight the puller into a space that has no room behind the cooler.
How Much CFM — Size to the Cooler
Fan airflow is rated in CFM (cubic feet per minute). Match the fan footprint to the cooler so you cover the whole core, then buy the highest CFM that fits. A fan that covers only the center of a large cooler leaves the corners dead. As a rough guide:
| Cooler / Use | Fan Size | Target Airflow |
|---|---|---|
| Small stacked-plate, light towing | 7 in | 400-600 CFM |
| Mid stacked-plate, regular towing | 9-10 in | 700-900 CFM |
| Large bar-and-plate, heavy towing | 10-12 in | 900-1,200 CFM |
| Dual-fan large core, max duty | 2x slim fans | 1,500+ CFM combined |
Slim fans are the right call for the tight space in front of a condenser. A thick high-performance fan that will not fit between the cooler and the grille is no airflow at all.
The Fans Worth Comparing
Slim 10-Inch Pusher Fan — The Standard Add-On
A slim 10-inch electric pusher in the 700-900 CFM range is the workhorse for an auxiliary trans cooler. Low profile so it clears the grille, draws modest current, and comes with the through-core mounting kit so you can secure it without drilling the cooler. This is what most tow-rig owners end up running.
Browse 10-inch slim pusher fans
High-CFM Curved-Blade Fan — Heavy Towing
If you tow heavy in hot country, step up to a curved-blade high-CFM fan in the 1,000+ CFM range. It moves a lot more air through a big bar-and-plate cooler, at the cost of higher current draw, so wire it through a proper relay. The curved blades are quieter under load than flat-blade fans.
Check high-CFM fans
Thermostatic Fan Controller Kit — Wire It Right
Do not run the fan off a manual switch you forget to flip. A thermostatic controller with a probe lets the fan come on automatically when transmission cooler temp climbs and shut off when it drops. Adjustable kits let you set the on/off threshold; an in-line probe kit clamps to the cooler line. This is the part that makes the whole setup work without you babysitting it.
Check fan controller kits
Relay & Wiring Harness — Don't Skip It
Electric fans pull real amperage and must run through a relay, not straight off a switch. A pre-made relay harness with an inline fuse saves you from melting a switch or a wire. Power the relay coil from the thermostat, the load side from the battery through the fuse, and you have a clean, safe install.
Check fan relay harness kits
What Goes Wrong — Five Failure Modes
- Fan wired without a relay. The switch or wire overheats and the fan quits, usually mid-grade when you need it most. Always use a relay and a fuse.
- Fan too small for the core. A 7-inch fan on a 12-inch cooler cools a circle and ignores the corners. Cover the core.
- Pusher mounted blocking the radiator. A thick fan in front of the condenser steals airflow from the engine cooling stack. Use a slim fan and confirm engine temps did not rise.
- No thermostat, runs constant. Running the fan all the time wears the motor and the bearings for no benefit. Trigger it on temperature.
- Mounting tabs cut the cooler. The push-through plastic ties saw into the fins over time. Use cushioned mounts and check them at every service.
Coolers, Lines & Fittings Ship Same-Day
A fan is only as good as the cooler in front of it. gearboxinsider.com stocks auxiliary transmission coolers, cooler line, AN fittings, and thermostatic bypass parts for tow builds. Same-day ship before 2pm Eastern, free shipping.
Shop Gearbox Insider →FAQ
Do I even need a fan on my trans cooler?
If your temps only spike in slow, heat-soaked towing and are fine on the highway, a fan solves it. If temps are high everywhere, the cooler itself is too small or the fluid is shot; a fan will not fix that.
What temperature should the fan turn on?
A common setpoint is to bring the fan on around 180-190 F at the cooler and let it drop the temp from there. Set it so the fan runs during the heat-soak situations and rests on the highway.
Can I tie the fan into the factory fan circuit?
Keep it on its own relay and thermostat. A dedicated circuit is simpler to troubleshoot and will not load the factory cooling system or its computer.