I am installing a tranny temp gauage. Which is the hot line to the cooler. Is it the line from the tail end of tranny, or is it the one from the center of tranny. I know I want the hot line to the cooler for the instalation. Thank you

 

On my 2005 Cummins with the 48RE transmission the line located toward the front of the transmission is the output line. You can easily see it going into the first cooler, then on to the front cooler and then back to the rear of the transmission case. There are many thoughts on where to tap into the line but I like it on the output so I can see instantaneous changes in transmission temperature. Don't be alarmed if it spikes quickly to 220 or so. Anytime the torque converter is unlocked like when driving really slow or backing up you will see higher temps. Also be aware that the transmission does not pump fluid in Park. Thus if you are seeing excessive high temps like 250 and want to pull over and let it cool down do not sit there in Park thinking it is circulating and cooling. It is not! Leave it in Neutral for fluid circulation.