Leaking Trans Cooler Line

2500HD 8.1 · January 28, 2009

Has anyone else had this problem? I just noticed that the trans cooler line has a slow leak on my 04 Avalanche and is leaking from the fitting. During the summer the oil cooler line on my 05 Denali did the same, but it seemed to stop.

Is this a common problem or design flaw with these lines? I just bought the Avalanche a month ago/600 miles ago (currently has 91K miles), and I drained the trans pan and added 3 or 4 quarts of Dexron VI. I was just wondering if the synthetic trans fluid could have loosen things up or seeped out of a seal?

alvocado · February 21, 2009

Has anyone else had this problem? I just noticed that the trans cooler line has a slow leak on my 04 Avalanche and is leaking from the fitting. During the summer the oil cooler line on my 05 Denali did the same, but it seemed to stop.

Is this a common problem or design flaw with these lines? I just bought the Avalanche a month ago/600 miles ago (currently has 91K miles), and I drained the trans pan and added 3 or 4 quarts of Dexron VI. I was just wondering if the synthetic trans fluid could have loosen things up or seeped out of a seal?

I'm not sure which fitting you are referring to but the crimped metal to rubber connections are more prone to leaking. I replaced my engine cooler lines last year after both started to leak where the metal lines connected to the rubber. My tranny cooler lines are fortunately still dry but similar in design. Dexron VI has no affect on the lines.

The lines aren't expensive but I did have to drop the transfer case to get enough clearance to run the new oil cooler lines.

ScottyBoy · February 22, 2009

If its leaking at the flare nut fitting where the line goes into the cooler, try tightening it. I remember my brothers old 90 chevy 2500 did this and all we did was tighten that fitting a bit more and that stopped the leak. Same exact thing happened on an older pontiac bonneville my other brother had. Just tightened the fitting a bit more and that was it. But those flare nuts are soft metal and easily stripped. (At least those two were) we did end up rounding off the corners and using vise grips to tighten them securely. I supposed a flare nut wrech would be better for the job.