Oil Cooler lines and Transmission Cooler Lines Leaking

Brendan Cosworth · January 9, 2016

Is there a decent how-to on this? I have a 6L-80 with the KNP package. I only ask because I've read that a monkey can do this, but then I've read that you need to move a motor mount and that book time is 4 hours. I'll be completing this in my driveway but I am not a total noob to mechanical repairs.

Parts weren't terrible at $93.24 for the lines, but I haven't climbed under the truck to see what I am up against. They are just sweating at this point but I want to replace them before I tow next summer.

CapitalTruck · January 28, 2016

In my 2wd GMT-800 it wasn't too bad. I'm not sure if 4wd would be worse. I didnt take any motor mounts or anything off. You just have to snake the old one out, remember the movements you took to get it out, and then put the new one in using those steps. I remember at one point having one end of the line wedged way up into the fan shroud to coaks the other end where I wanted it to go. When I added the KNP package to my truck (using OEM parts) I almost started to cry it was so frustrsting. Like others with the OEM part, mine started leaking after a while. The second replacement was much easier.

musselman · July 13, 2016

Noticed the other day that the lines on my 2013 are leaking, both the engine oil cooler and trans cooler lines. Had the engine oil lines replaced under warranty but the transmission lines are not covered? These lines are the exact same except for the size, I don't understand why they aren't covered. I guess GM prefers to replace the whole transmission when all the fluid leaks out of the lines. This is something that needs to be covered under warranty, everyone I know with a GM truck has had these replaced, it is a major problem.

MaverickZ71 · July 14, 2016

Noticed the other day that the lines on my 2013 are leaking, both the engine oil cooler and trans cooler lines. Had the engine oil lines replaced under warranty but the transmission lines are not covered? These lines are the exact same except for the size, I don't understand why they aren't covered. I guess GM prefers to replace the whole transmission when all the fluid leaks out of the lines. This is something that needs to be covered under warranty, everyone I know with a GM truck has had these replaced, it is a major problem.

All lines are covered during the 3 yr/36,000 mi bumper-to-bumper warranty. But after that warranty expires, your truck is covered by the powertrain warranty, and you have to read the owner's paperwork closely on that one, as there is a LOT of powertrain stuff not covered by the powertrain warranty! Such as oil lines being covered and transmission lines maybe not being covered by the powertrain warranty. It's not very logical, but it all seems structured to save the General money.

royalsward · July 17, 2016

Take a screwstyle hose clamp, loosen it all the way and then put it back together over the crimp joint. I did this on my transmission cooler lines 3 months ago and no more leaks. I am an ASE master technician and have replaced several of these and just did not feel like replacing my own and did this as a little experiment.

66and10 · January 3, 2017

Just finished mine yesterday. I had a leak on one of the trans cooler lines that was leaving a small puddle once parked. While investigating, I also found that one of the oil cooler lines was leaking, though at a much slower pace. Both leaks were at the crimp joints. I picked up a complete set of lines (3 trans and 2 oil) from the dealer for $240.

The trams cooler lines were not too bad, but did take some trial and error to get them out. Did not require removing anything other than the radiator cover and the plastic skid plate behind the bumper. Done on my 4 post lift, took me about 2 hours.

The oil lines cannot be removed without removing the driver side motor mount. In order to get to the bolts for the motor mount, I first had to remove the heat shroud on the exhaust manifold and remove one bolt on the steering shaft to pivot it out of the way and zip tie there. The motor mount was not fun to remove, but once out (and the front drive shaft was disconnected from the front axle yoke), removing the oil lines and replacing with the new one was about a 10 minute job. All told I had 6 hours into the oil line replacement, with a 15 minute break for a sandwich. Since the only way I had to lift the engine off the mount was with a cherry picker, this job was done with the truck on the ground, and me crawling under it. 90% of this job is done from the top side, so this is not a big deal. The only work under the truck was to remove the 4 screws on the driveshaft u-joint straps and the 2 screws holding the oil line manifold to the block.

Sorry, I did not take any pics.

diy_darryl · January 3, 2017

Just found this last weekend on my 2009 4wd Sierra transmission cooler line. It was $23 at the dealer for the part. I needed the upper one at the tranny connection and could see no way of getting at it without dropping the tranny down, NO THANKS! Took a Pipe Cutter and cut the flex section out where it was leaking and put a piece of 3/8" id hose on it with hose clamps. Not leaking a drop so far!

Charles Ronk · November 11, 2017

Is this a new problem with GM hoses? I have a 1997 GMC Jimmy 4x4 that in 2015 developed an oil leak. Without looking close I assumed it was the Oil lines to the remote filter mount. I replaced the 18 year old GM lines with Dorman lines. I quickly found out that it was actually leaking from a crack in the remote filter housing. I figured as big of a pain as it was to remove the lines I would just leave the Dorman lines on and discard the old GM ones. Less then 2 years later oil is leaking again. This time I look close and it is leaking out of 3 of the 4 connections where the rubber portion is crimped to the line. So I am not sure how good GM lines are but these Dorman's were crap. The only good thing is a lifetime warranty, but as big of a pain as these are to change if they leak again I will be looking me up some Ac Delco replacements.

swathdiver · November 11, 2017

No, they wear out. I've had these oil cooler lines fail on my 1980s Oldsmobile and Buick autos but after learning the hard way, an eye is kept on them and replaced before they become a problem. Going to replace them soon on my truck too as they're sweating. Steel braid and fancy anodized fittings would be better.

bgbdwlf2500 · November 13, 2017

One of my trans lines was leaking, I just used a tubing cutter and cut the pot metal crimps off. I made sure that the new rubber line I bought from autozone was long enough to put 2 hose clamps on each end. almost a year and about 15 bucks later, its still dry.