When it comes to understanding the transmission cooling system of your GM car, truck or SUV, it’s always important to know which transmission lines are the send (hot fluid) and return (cooler fluid after flowing through the cooler). Based on which is which, you will know which port on the factory cooler within the radiator will be routed to an external transmission cooler if you plan on installing one.
This 4l60e transmission cooler lines diagram provides an easy to follow example of how your 4l60e’s cooling path works.
4l60e Cooler Line Flow Direction
The 4l60e transmission cooler line flow is very easy to follow. As the gif above shows, the bottom line is the hot line which sends warm transmission fluid out to the factory trans cooler within the radiator at the lower port in most cases. FYI, some vehicles have the factory cooler on the bottom of the radiator, but simply follow the lower cooler line coming from the transmission to find the hot or cooler inlet line.
Once the hot fluid flows into an through the factory cooler, it then exits at the top or other side to the cooler outlet or return line, which is the top line on your 4l60e. This would be the line you’d tap into if you were looking to install an aftermarket external transmission cooler.