Hello,
in my 1988 gmc sierra stepside 4x4 with a 350 and 700r4 w/ stock radiator I was wondering what tranny line from the radiator is the output. I am going to install an aftermarket cooler and run it along with the one that already goes through the radiator. I hope i gave you all the info you need , if not just reply and ask for more. Also i have an oil cooler going through the radiator as well if that helps any.
Thanks for the help,
-Dave
:usa:

You want to run the fluid to the cooler first then through the radiator.
So you want the presure side not the return.
To find out which is which just bust a line off and hold it over a can and have someone start the engine for a second.
The one that has fluid coming out when the engine is running is the one that you will run to the cooler, then the other line from the cooler to the empty hole in the radiator.
By the time that the fluid returns to the tranny it will be around 170-200*. perfect operating temp.

Thanks for the help,
And you are sure thats the better for it to go through the cooler first? I just wanted to double check. I took the other advice from my friend but then again he just has a tranny cooler on his truck, so he probably isn't sure and i am leaning your way, it sounds like it will work better. And i have this little fan that fits on the cooler, today i am going to see if it is waterproof and if it is , do you think it would be beneficial for the cooler?
Thanks for your help,
-Dave

I would skip the radiator cooler. If your temp is lower than the rad - the rad will just bring it up. My radiator guy doesn't use them and told me not to.

That is what it is supposed to do.
The cooler will get rid of the high temp and the radiator will bring it to operating temp.
For an automatic tranny running it to hot is bad, and too cool is not good either.
around 200* is what a tranny runs best at.

An easier way to determine the pressure line instead of disconnecting and making a mess is to.......
When the truck is cold, start it up, feel the lines going into the radiator, the line that gets hot is the pressure line........:skull:

Thanks for that tip. sounds a little easier.
-Dave