40K Transmission Cooler Kit with Thermal Bypass Valve

This is the 40,000 GVW low-pressure-drop cooler that gets bolted in front of the condenser on tow rigs, packaged with the external thermal bypass valve (708-4739P6) that the plain LPD47391 cooler does not include. The cooler core and the bypass valve work as one assembly: the valve tees into the transmission cooler line ahead of the core, and until the fluid comes up to operating temperature it routes that fluid around the cooler instead of through it.

That matters on a cold start and on a light-load winter commute. A big auxiliary cooler with no bypass will hold ATF below operating temperature for miles, and cold fluid is thick fluid - it drags, it shifts late, and it takes longer to build line pressure. With the bypass in the circuit, the transmission warms up on its own schedule and the cooler only sees flow once there is real heat to pull out. Hook a trailer to it in July and the whole core is working; run it empty in January and the fluid is not being over-cooled.

The core itself is the familiar low pressure drop design rated to 40,000 lb gross vehicle weight - a lot of surface area without the back pressure a restrictive tube-and-fin core builds, so the transmission still gets the flow it needs. Mounting hardware, bolts and brackets come in the box. Plumb it in series with the factory cooler on the return side, use the supplied hardware rather than push-through nylon ties through the radiator fins, and check the line routing for clearance before you tighten anything down. Package measures 25.5 by 10.5 by 2.93 inches and the kit weighs 6.24 pounds.