Will L.
Well-Known Member
4L80E transmission cooling line bypass valve is a part all hmmwv and civilian Hummer, Hummer H1 have (idk about H2, H3).
On hummernetworkforum.com the discussion about this valve came up. I never noticed it on any GM rigs, or anything that the 4L80E went into outside of a hmmwv/Hummer. It’s possible that because I never had to replace one I simply never paid attention. I saw it on my Hummer, read about it and forgot about it basically.
The running theory is that when temps are so low the atf is thick and not flowing well so this device was added for extremely cold environments or maybe if a cooling line gets piched off roading and restricts flow- then this bypass valve simply sends the hot output atf directly back into the transmission as to not burn up the transmission right away. Better hot fluid than no fluid.
If anyone can find any vehicle this is on besides a hmmwv/ Hummer: please share the vehicle info, part number, LOVE PICS always, etc to teach me and others.
The two lines on this are simply spliced into a “T” that is interrupting the two cooler lines within about a foot of leaving the transmission.
Just because he isn’t on here as often as before, gonna bother @THEFERMANATOR for the extensive trans knowledge.
![IMG_1211.png IMG_1211.png](https://www.thetruckstop.us/forum/data/attachments/77/77621-759544494338544b89fb343c975cbe83.jpg)
On hummernetworkforum.com the discussion about this valve came up. I never noticed it on any GM rigs, or anything that the 4L80E went into outside of a hmmwv/Hummer. It’s possible that because I never had to replace one I simply never paid attention. I saw it on my Hummer, read about it and forgot about it basically.
The running theory is that when temps are so low the atf is thick and not flowing well so this device was added for extremely cold environments or maybe if a cooling line gets piched off roading and restricts flow- then this bypass valve simply sends the hot output atf directly back into the transmission as to not burn up the transmission right away. Better hot fluid than no fluid.
If anyone can find any vehicle this is on besides a hmmwv/ Hummer: please share the vehicle info, part number, LOVE PICS always, etc to teach me and others.
The two lines on this are simply spliced into a “T” that is interrupting the two cooler lines within about a foot of leaving the transmission.
Just because he isn’t on here as often as before, gonna bother @THEFERMANATOR for the extensive trans knowledge.
![IMG_1211.png IMG_1211.png](https://www.thetruckstop.us/forum/data/attachments/77/77621-759544494338544b89fb343c975cbe83.jpg)