Which cooler line is return?

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7,672
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Hudson, NH
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2005 Chevy Classic which is the same as the 5th gen Malibu. Wondering if the line I circled is the return line. Or if it's the bottom one . Want to use it for an ATF exchange. [Linked Image]
 
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16,675
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NH
Pull the line and start the engine, and see what direction the mess is shooting? Might want to do that Walmart instead of home though. LOL
 
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339
Location
Alaska
Hm. Well, regardless of whether you're at home or Walmart, I would trace the lines. The top one looks like A/C to me, and the bottom one looks like it might be transmission fluid. Might be worth doing some Google searches, or even picking up a Haynes manual.
 
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7,672
Location
Hudson, NH
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Originally Posted by Donald
Do you have a IR thermometer? Return will be cooler. Typically upper is supply and lower is return.
I just tried that and it says the top one is warmer. But when I tried the truck which I know the top one is the return that's also warmer. Oh well I guess I'm putting two hoses in place just in case
 
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16,675
Location
NH
Originally Posted by LeakySeals
Maybe because it's cold here the opposite is happening and the the return will be warmer as it passes through the radiator?
Could be. Does the transmission have a thermostat? My truck has one, and won't send ATF to the cooler if it's below a certain temperature--part of the fluid change involves bypassing the t-stat (locking it open). Have you hit up any specific forums? Sometimes guys will post DIY's on how they did whatever work, complete with pictures.
 
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New York City
FWIW, The return trans cooler line on my DTS is the top one. When I did an ATF drain and fill, I screwed a fitting into the top connector and ran a hose to a bucket.
 
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7,672
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Hudson, NH
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Well I won't know today. Because my hose set up won't work on this car. I need a different fitting. It's a flange like a brake line. I'll have to get that kind of fitting to attach to my hose [Linked Image]
 
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Location
Maryland
Originally Posted by A_User55555
FWIW, The return trans cooler line on my DTS is the top one. When I did an ATF drain and fill, I screwed a fitting into the top connector and ran a hose to a bucket.
Correct
 
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Under the Hood
Originally Posted by Kestas
Once you figure it out, put markings on the lines so you don't need to figure it out next time.
I agree, your future self will thank you. Draw a sketch of the Radiator and Transmission with any hoses. Then add 'arrows' -> showing direction of fluid flow. Knowing the direction of flow would also help if you ever install an Inline Filter.
 
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1,781
Location
Wisconsin
from what Information I gathered usually the top line is the return line. and now that I type this I remember when flushing the trans fluid out of my thunderbird that is the line i unhooked to drain out the old fluid while running it, I hooked up a hose around the fitting on the radiator to flush out the fluid.
 
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