6L80e fluid return line

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My Jeep JK Wrangler now has a GM LS 5.3L engine and a 6L80 transmission. I'm upgrading the tranny fluid cooler and want to make sure I have things flowing the right way. Which line is the fluid return line, top or bottom at the transmission? I thought it was the top line but found some conflicting information on the interweb.

Thanks!
 
Originally Posted By: userfriendly
Bottom line from transmission to top of rad, return line is from bottom of rad to top of transmission.


That makes good sense. It would be easier for the fluid to flow down through the radiator--rather than flow upwards.
 
Originally Posted By: Merkava_4
Originally Posted By: userfriendly
Bottom line from transmission to top of rad, return line is from bottom of rad to top of transmission.


That makes good sense. It would be easier for the fluid to flow down through the radiator--rather than flow upwards.


Hmm, B&M says the input should be on the bottom on their Supercoolers if the connections are on the side. Seems fill from the bottom would ensure the cooler is filled where top feed maybe not. Come to think of it I guess it would depend on the type cooler. Tube and fin wouldn't matter where on a stack plate cooler it might.
 
Originally Posted By: userfriendly
Bottom line from transmission to top of rad, return line is from bottom of rad to top of transmission.


The cooler feed/out is the TOP cooler line, The BOTTOM line is the return/lube on a 6L80E WHERE they come out of the bellhousing.
 
Now you guys got me all kinds of confused.
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Originally Posted By: Merkava_4
Originally Posted By: userfriendly
Bottom line from transmission to top of rad, return line is from bottom of rad to top of transmission.


That makes good sense. It would be easier for the fluid to flow down through the radiator--rather than flow upwards.


Usually the bottom of the radiator cooler is the inlet. You want the fluid in the cooler longer so the heat is transfered. If it flows too quickly(from top to bottom), the transfer of heat is minimized. On my Buick, the bottom line was the fluid source into the radiator cooler.Not to be confused with the coolant which has far less pressure behind it.
 
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I just R&R'd a couple of T350s 'n 400s a month ago. Before pulling them, I disconnected the top line from the radiator, put a hose on the end into a 5L oil jug and started the engines.
I got about 3 liters out that way, which otherwise would have ended up on the ground or driveway.
If in doubt, take both lines off with hoses into containers.
 
Originally Posted By: Trav
Find the line on the transmission from this slightly outdated chart and follow it to the radiator if in doubt.


I found this chart. I also found others that indicated the opposite, hence my confusion. Guess I'm going to have to pull a line and do the bucket test. If it matters my transmission is supposed to be a 2013.
 
#8, Cooler Feed (Fluid OUT to cooler) Top line at the transmission.
#9, Center Lube (Fluid RETURN from cooler) Bottom line at the transmission.

I checked a 6L80E GM service manual & a 6L80E ATSG manual, Same picture in both!

All GM/Hydramatic RWD units are this way with the exception of the TH200 & 200-4R which are backwards.
Late 4L80E's have Front & Rear cooler lines, Front is feed, Rear is return.

C6yv2PH.jpg
 
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