When installing an external transmission cooler, should I route the fluid through the cooler 1st and then into the rad or take the discharge from the rad and run it through the cooler then back to the trans?

me personally I dont think it is a big deal either way but others who know more than me have posted their preferences & why, iirc something about heating up cold fluid in the winter. I bypass the rad cooler entirely just because if there's a leak in the lower tank I'll see trans fluid in the coolant or coolant could get into the trans. I'd use the largest cooler that will fit & reportedly a "stacked plate" type cooler is more efficient

Through the factory rad cooler first,then the aux cooler,back to the trans.

Thanks - which line is the supply line and which one is the return on a BB/727?

the line at the front of trans is pressure line out to rad.

wont matter which side the line goes to on the rad,the other rad line to cooler and back to rear line on the 727.

***if you are in sub 0* weather you would run to cooler then to rad back to trans. this keeps the fluid up to temp in the freezing cold.

use the biggest cooler you can mount or 2 smaller ones in tandom. if they are not in front of rad,and say in a fender well,you want to add a fan to them for airflow.

This might sound crazy, but would it be counterproductive to mount it behind the radiator? I've got so much room to work with it's ridiculous ('66 Chrysler 300) I could even mount it 6" in front of the radiator as well. Maybe I'll experiment - get a digital infrared pyrometer and mount the aux. cooler in various locations and zap the lines w/ the pyrometer and see what works best

out front is best,behind rad will work.

a dead space void of airflow can work with ducting or fan.


I have mounted a cooler behind the core support on my truck and cut a hole to let ram air flow thru cooler. replaced the bottlejack and holder on pass side inner fender.


not crazy at all. results do vary and that is one way to see the results.

in front of rad gets cool air

behind the rad gets hot air. = counter productive..

use the least amoung of rubber hose. make sure its transfluid/heat compatable..

If you mount it in front of Rad, keeping space between the two is better still. You wont get the radiant heat from the rad and it will allow air to pass behind it into the rad as well. If at all possible, dont mount it to the rad as this can damage the rad tubes and fins.