E4OD cooler line check valve
 

Hi there. Looking to put new transmission cooler lines on my truck. How important is the return fitting on rear of the transmission that returns fluid from the cooler line into the trans? I have one off a spare transmission and it looks as if it is a one way check valve to only allow fluid to enter trans. Just wondering if it is necessary to use? Right now it is the only thing holding me up.
Thanks, Brennan

Could it be a bypass? It has a tube that connects the In and the Out lines. If the Out line gets restricted, like a tube kinks or cooler gets clogged, it routes the fluid back into the In port.