I'm putting in a Hayden Rapid-Cool Tranny Cooler and need to know which line is the return line for the tranny fluid. I would assume that it's the lower line on the radiator, but I need to make sure. I usually guess wrong in these situations. :(

Update your sig with your truck info. We can't help if we don't know what ya got;)

1994 2500 HD with the 6.5 TD, "F" Vin.

Should have a "small" factory cooler in front of the rad. If it does, you hook into those lines and discard the factory one, or you could put them in series.

Should have a "small" factory cooler in front of the rad. If it does, you hook into those lines and discard the factory one, or you could put them in series.

I wish it was that simple, but it ain't. :(

The truck never came with a factory tranny cooler. And that confuses the hell outta me. It's a 2500HD with a 6.5TD and it didn't come with a tranny cooler. :confused: It has an oil cooler though. :)

I need to hook the cooler in line with the tranny fluid return line. I still can't figure out if it is the fitting for the return line is the upper fitting in the radiator, or the lower fitting. Can some one give a brutha a hand please? :lol: :iamlost:

External cooler is an option, not standard issue.

Check your lines when you start the truck up after it's been sitting a while and see which one is warmer. The warm one is coming from the tranny. Someone will be able to tell you the correct routing, but a physical check will guarantee the right results

SnowDrift

If I had to make a guess I would think the lower is the input to cooler. I am just thinking here but seems if upper was input you would get air pockets in line. I am thinking the lower would have to be input and this would completely fill the cooler from bottom up. I dunno I may be overthinking this or something. I agree about checking on heat at the two lines. You could also use a thermometer (like IR or something) to see which line is cooler than the other after driving. the cooler one would be output. Post what you find out so we will all know the answer the next time someone asks. Also I need to install another cooler on mine too so I would be in the same situation.

The fluid enters at the lower end of the cooler and exits at the upper end (top line). Verify with a "feel" of the lines. A heat gun "Laser Thermometer" would help. All the trucks I've seen with external cooler were hooked up with the cooler in series with the top line coming out of the radiator. Hope this helps.

I just went out and checked my '01 gas truck, it read 95 degrees on the bottom line and 86 degrees on the top line. Checked with the Raytek non-contact thermometer.

Seems to me that you would want the cooler in series with the bottom line then. I think there was a concern with the cooler getting the fluid too cool if it is plumbed in the output side of the radiator cooler. If it is plumbed in the input side, the hot oil from the tranny will go to the aftermarket cooler first then to the radiator then back to the tranny. Having the radiator last will heat the oil to radiator temp if the oil is too cool. (prevent thermal shock)

Maybe I am overthinking a simple thing again? what do you think?

Jperry, I've always been told the same thing and it makes sense

A good tranny cooler will not make the fluid too cool so that it shocks the system with cold fluid. Coolers like the ones "Long" makes use a series of orifices which the are in each row to determine how much of the cooler the fluid actually goes through by how hot the fluid is. The hotter it is the smaller the hole the fluid will easily flow through. I have found that these coolers keep a very consistant temp.

Wow, I just re read that. I think I lost myself in that explanation. Maybe be best to check out longs website

Do you happen to have a website? Think ya might have lost me on that one too. I can understand the different size holes but seems the hot fluid will just go to the one of the least resistance. If I am thinking this correctly

My solution was to install a Deraile one from Summit, with thermostat controlled fan that only kicks in fan if pan temp >170F

My solution was to install a Deraile one rated for up to 25K tow load from Summit, with thermostat controlled fan that only kicks in fan if pan temp >170F

http://www.dana.com/Automotive_Systems/images/PDFs/TC_Brochure_2004_Website.pdf