Transmission cooler lines: which is output and which is input?
 

2003 Lincoln Town Car. I assume that transmission fluid flows OUT from the transmission through a line to the transmission cooler and then flows BACK/INTO the transmission through a return line?


How can I find out which transmission cooler line is output and which transmission cooler line is input?

disconnect one and put it in a bucket and crank the engine.

Do I need to put the car up on jack stands and look underneath it? Do the transmission cooler lines indicate which is outflow and which is inflow to the transmission?

Start the car cold and see which line gets warm first, that should be the inbound line to the cooler from the transmission. On a warm engine the cooler line would be the return to the transmission. I've seen the flow both ways on various cars so I'm not comfortable in saying which is which (upper vs. lower) on that car. I'd rely on temperature.

Thank you, that makes sense. I would think that using a temperature gun would be helpful in making the determination.