I have a 89 chevy pick up with 4.3 liter engine. Where the transmission lines go into the radiator I need to know how the fluid flows. Is the bottom connection returning fluid to the transmission or is the fluid coming from the transmission? I would like to add after market cooler and need to understand the flow. Also does the after market cooler go before radiator cooler or after?

 

The fluid generally flows from the top to the bottom but you should be able to feel the temp difference in the lines.

 

You can always disconnect 1 line. Hold your finger over the line and put another finger in the opening in the radiator. Have some one bump the starter untill you see which way the fluid is flowing and you will not be guessing.

It works every time.