at the radiator, which line is the transmission sending and which is return?

It's holding me up on finishing the car... I need to get this cooler installed. Anyone know for sure? I have gotten a lot of conflicting guesses, but noone can tell me with complete 100% certainty.

 

Try this:

Disconnect one line, have the missus start the car for just a second. If it squirts out of the hose, it's the high side. If it squirts out of the radiator, the hose will be the low side return.

 

I'm picky so I would want to be 100% sure also... But does it really matter which line goes in where? It just completes the path through the cooler right? So it shouldn't make a difference.

 

on a 98 chevy truck the bottom feeds the radiator from the tranny.

 

It makes a difference because the oil from the high side should be passed through the air cooler first, then passed through the water cooler in the radiator second. This enables the transmission fluid to shed high heat more efficiently in the auxilliary oil cooler, then maintain a more even temperature based on the coolant temperature. If you do it backwards, you shed the excess transmission oil heat into the coolant (rather than the atmosphere)before it goes back into the engine, then cool the transmission oil to a low temperature based on the current air temp of the day. Coolers work best when there is a large temperature differential between the air and the oil inside.

The other theory is to forgoe the use of the radiator chiller altogether and run straight off the auxilliary cooler to get the transmission oil temperature as low as possible.