Which transmission line to the radiator is which?

[RossT]

Which one flows to the radiator and which one is the return line to the transmission?

 

1500HD 2003

 

edit: I was just thinking.. If the truck came with the heavy duty transmission cooler, does it even have lines to the transmission? If not, which line to the cooler is the return line and which line flows to the cooler?

 

Thanks!!

[robsawatsky]

I'm presuming this is still valid for your model year. Front/rear and fittings refer to the fittings on the transmission.

 

4L80E (1997 & later)

 

Fitting Location

Thread Size

Flow Direction

 

Rear

¼” Pipe

Return/in

 

Front

¼” Pipe

Cooler feed/out

[DeezBlueZ]

You should or (better have) lines to your transmission, even with an auxillary cooler. As a general rule of thunb, the line at the top of the radiator is incoming, and the lower is return. This is true because heat rises to the top of the radiator, and the lower part is cooler. If you want to experiment, you could take a line off of the radiator, bump the engine on then right back off to see for shure...but it can be a little messy.

[RossT]

Thanks a bunch guys!!

 

(I meant to say if my turck has the auxillary trany cooler, does it still have lines to the radiator in addition to the cooler).

[robsawatsky]

Yes, if you have the auxiliary cooler the lines still go through the rad. One reason is that in cold weather the rad tranny "cooler" will actually warm the tranny fluid to keep it from getting overcooled.