Wehrli 17-19 Chevrolet 6.6L L5P Duramax Upper Coolant Pipe - Illusion Purple

Stop Fighting A Factory Rubber Hose That Was Never Built To Last

The OEM upper coolant hose on the L5P Duramax is a known weak point that softens, cracks, and eventually fails under sustained boost and heat cycling. The Wehrli WCF100742 replaces that factory rubber section with a mandrel bent aluminum pipe finished in Illusion Purple powder coat, giving your cooling system a permanent upgrade instead of a wear item that needs replacing again down the road.

Key Features

• Mandrel bent aluminum construction replaces the failure prone OEM rubber upper coolant hose
• Illusion Purple powder coat finish with WCFab logo tag for a finished underhood look
• Direct replacement for GM part number 84094878 on 2017 to 2019 L5P Duramax trucks
• Ships complete with silicone boots and T-bolt clamps for a proper factory style seal
• Designed to work with the OEM GM radiator for a bolt in fit without cutting or splicing
• Eliminates a common source of coolant seepage and hose collapse under heat cycling

Fitment

Fitment applies to trucks equipped with the 6.6L L5P Duramax Turbo Diesel V8. Confirm your engine option before ordering, since the L5P was only offered as an upgrade over the standard gas V8 on these model years.

Specifications

What's Included

• 1 aluminum upper coolant pipe in Illusion Purple powder coat
• 2 silicone boots
• 4 T-bolt clamps

About Wehrli Custom Fabrication

Wehrli Custom Fabrication builds Duramax specific intake, cooling, and piping upgrades out of its Illinois shop, with every coolant pipe and intercooler pipe mandrel bent and finished in house. The brand is a mainstay in the diesel truck community for parts that solve real factory weak points instead of chasing horsepower numbers alone.

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Frequently Asked Questions

The WCF100742 is a Wehrli Custom Fabrication aluminum upper coolant pipe built for 2017 to 2019 GM trucks with the 6.6L L5P Duramax. It replaces the factory rubber upper coolant hose with a mandrel bent aluminum pipe and ships with silicone boots and T-bolt clamps for installation.

No. The WCF100742 is built specifically for 2017 to 2019 trucks. Wehrli produces a separate upper coolant pipe for 2020 and later L5P trucks since the routing and boot shape changed for that generation.

Wehrli designs this pipe to work with the factory GM radiator. Aftermarket radiators can shift hose routing and clamp positioning enough to cause fitment issues, so confirm compatibility before installing on a truck with a non OEM radiator.

It replaces GM part number 84094878, which is the factory rubber upper coolant hose that runs between the radiator and the thermostat housing on the L5P Duramax.

Yes. Every kit ships with two silicone boots and four T-bolt clamps so you have everything needed to complete the swap without sourcing extra hardware.

Most owners complete the swap in a driveway with basic hand tools. The job involves draining a portion of coolant, removing the factory hose at the radiator and thermostat housing, and clamping in the new pipe, typically in under an hour.

The factory hose is a rubber section that sits close to heat sources and cycles through repeated expansion and contraction. Over time it can soften, crack, or collapse internally, which restricts coolant flow and can lead to overheating under load.

Wehrli offers the WCF100742 in several powder coat finishes. This specific listing is the Illusion Purple finish; check the brand's other listings for alternate color options.

Install Instructions

1. Allow the engine to cool completely before starting, ideally overnight.
2. Slowly remove the cooling system cap to relieve any residual pressure.
3. Drain about one gallon of coolant into a clean container from the radiator drain on the passenger side lower corner.
4. Loosen the clamp on the factory upper radiator hose at the radiator and remove the hose.
5. Repeat at the thermostat housing to fully remove the factory hose from the truck.
6. Install the silicone boots onto both ends of the new aluminum pipe and loosely fit the T-bolt clamps at the radiator and thermostat housing.
7. Slide the pipe into the boots at both ends, then align the boots and clamps for proper logo placement and clamp access.
8. Tighten all T-bolt clamps, refill the cooling system, and start the truck to bring it to normal operating temperature.
9. Check closely for leaks before driving and retighten any clamps as needed.
10. Recheck the coolant level and all clamps after the first few heat cycles to confirm a leak free installation.