Does it Really Matter if Transmission Cooler is Installed Before or After OEM Cooler

Updated 10/22/2025 | Published 11/03/2021

Question:

I watched 2 videos for 2011 and 2014 odyssey They seem to install on different lines in each video. I felt the two lines and found what felt like the warmer of two. After the install it seemed to be opposite of previous findings. Ive been looking for more definitive info on flow direction but getting split info again. Does it really matter if the fluid goes through the new cooler after the oem cooler or could it go vice versa. Its between curved/ looped currently new install or straighter short hose original

asked by: Jon C

Expert Reply:

Your most ideal routing for a transmission cooler would be from the OEM cooler to the aftermarket cooler if the OEM cooler is integrated into the radiator since the proximity to the radiator fluid might end up warming up the fluid after the aftermarket cooler. If the OEM cooler is separate from the radiator it makes no difference which you use. The way to tell easily requires a buddy you trust.

When the vehicle is cold grab both of the transmission lines from the OEM cooler. Have a buddy start the vehicle and put the vehicle in reverse with the brake pressed firmly. Now have him push down on the accelerator to point the RPMs climb and there's an obvious strain on the vehicle without moving. You should feel one of the lines get significantly warmer than the other. That's the line to use.

expert reply by: Jameson C

Hale

10/22/2025

Are you certain your advice is correct? The first line to warm is the one coming from the transmission to the OEM cooler. The outlet line will be cold until the engine warms enough open the engine thermostat to circulate engine coolant.