4L80E Cooler line size 3/8" or 5/16"

[ZEKE68]

Who has put a 4L80E into their truck, and what size cooler lines did you use. Seems the later 4L80E transmissions used 3/8" lines and I am wondering if its safe to use the stock 5/16" cooler lines with the 4L80E.

[aggie91]

3/8 is what we used.

[First c10]

I used russell power flex -6AN on my 4L60E to the radiator and cooler

Hulk build Post 593 and 594

[racecougar]

Originally Posted by First c10

I used russell power flex -6AN on my 4L60E to the radiator and cooler

Ditto.

[ZEKE68]

Have found that GM used 5/16" cooler lines on the 4L80E until 1998. They must have gone to 3/8" when they moved the return line to the middle of the transmission case. All the radiators I have found for my 67 to 72 truck have 1.2" - 20 threads for 5/16" cooler lines so there will be some restriction at the radiator even if I run 3/8" lines to it. Thinking about splitting at the radiator and adding an aftermarket cooler in parallel to keep the flow up. Since GM ran 5/16" lines on the 4L80E in the early years I assume that unless I work the transmission hard I would be ok even if I stayed with the 5/16" lines.

[BR3W CITY]

In general for almost any automotive system; bigger lines can be used in place of smaller lines (fuel, oil, trans, coolant etc). Smaller (narrower) lines in almost any of those systems will create a restriction point, and depending on which system, will have different negative effects; cavitation, reduced flow, increased pressure where pressure is not desired, foaming, increased heat.