Replaces the leaking factory cooler lines on 2017-2019 Silverado and Sierra 2500HD/3500HD L5P Duramax with 5/8 inch hose and -10AN fittings.
If your 2017, 2018 or 2019 Silverado or Sierra 2500HD or 3500HD with the L5P Duramax is dripping red fluid near the front of the frame rail, the radiator or the passenger side of the bell housing, the transmission cooler lines are the usual suspect. This kit replaces the complete factory cooler line run on the Allison 1000 with three 5/8 inch ID reinforced hydraulic hoses and -10AN ends, so you fix every crimp and connector at once instead of chasing the next one.
The Allison 1000 sends hot fluid out of its To Cooler port, through a cooler section inside the radiator tank and through the separate transmission cooler mounted ahead of the radiator, then back into the From Cooler port. That return flow is also what lubricates the geartrain, so the lines are not a side circuit you can ignore. On the L5P the factory run is several hard-line sections joined with crimped hose and quick-connect ends. Those joints are where heat cycles and vibration eventually win. Because there are six ports involved (two at the transmission, two at the radiator, two at the cooler), this kit includes six 7/8-14 O-ring to -10AN adapters so every connection becomes a threaded, serviceable fitting.
Clean the area with brake cleaner, drive until the fluid is hot, then look again with a light. A cooler line leak starts at a crimp or connector and runs downhill, so trace the wet trail to its highest point before buying anything. Check the level hot, not cold. If the truck has already shown slipping, flare or a stored code, read our Allison 1000 limp mode guide before you assume low fluid was the whole story, and pull codes with a capable tool like our heavy duty truck scan tool for Allison transmissions.
This listing fits 2017-2019 Chevrolet Silverado and GMC Sierra 2500HD and 3500HD with the 6.6L L5P Duramax and the Allison 1000. It does not fit the 2011-2016 LML or the 2006-2010 LBZ/LMM, which use different routing and fitting sizes, and it does not fit 2020-up Duramax trucks, which moved to the Allison 10-speed. Confirm the engine code (the eighth VIN digit is the engine code on GM trucks) before ordering, or send us your year and VIN and we will check it. You can browse every part we carry for this unit on our Allison 1000 parts page.
With the front end apart is a good time to service the transmission too. Our Allison 1000 fluid and filter service guide covers capacities and intervals, and a double-deep spin-on filter is an easy add while the fluid is down.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. It is built for the 2017-2019 L5P Duramax with the Allison 1000 only. The LML uses a different line layout, and 2020-up Duramax HD trucks use the Allison 10-speed, which has different ports. Send us your year and VIN if you are unsure.
No cutting of the truck is required. The six 7/8-14 O-ring to -10AN adapters thread into the factory ports at the transmission, radiator and cooler. Many installers cut the old factory lines into sections only to make removal easier.
Use an Allison-approved fluid. Allison now recommends TES 668 for the 1000 Series, and a TES 295 synthetic or the Dexron VI that GM specifies for these trucks also works. Top off and check the level hot at 160-200 F.
Expect to lose what was in the old lines plus some from the cooler and radiator section, usually a few quarts. Have at least a gallon on hand, refill, run the engine and then check hot, since the new hoses hold slightly more than the factory lines.
It can be, if the level dropped far enough. Fix the leak, correct the level and recheck. If slipping or codes continue with a full, hot level, the problem is inside the unit and should be diagnosed before more parts are installed.
