Wehrli WCF100155 Billet Coolant Heater Core Firewall Fitting 1999-2023 GM Duramax

The Wehrli WCF100155 is a CNC machined billet aluminum coolant heater core firewall fitting built as a direct-fit upgrade for 1999-2023 GM trucks, SUVs, and vans from the earliest Silverado 1500 gas engines through every generation of 6.6L Duramax diesel. The factory GM plastic coolant heater core firewall fitting (OEM part number 15032062) is a well-documented failure point on these platforms: the plastic cracks, warps, and degrades under years of heat cycling and coolant pressure, leading to slow drips that can escalate into full coolant loss. The WCF100155 eliminates that vulnerability with a CNC machined billet aluminum body and a double O-ring seal that holds where the factory plastic cannot. Made in the USA by Wehrli Custom Fabrication in DeKalb, Illinois, the WCF100155 is backed by a 12-month limited warranty covering defects in material and workmanship.

Why the Factory Plastic Fitting Fails and Why WCF100155 Is the Fix

The OEM GM coolant heater core firewall fitting is molded from plastic because it is cheap to produce and adequate when new. Over the service life of a truck that may see extreme temperature swings from -20 degrees to engine operating temperature repeated thousands of times, the plastic fatigues. Here is what leads to failure and why the WCF100155 addresses each cause:

• Plastic cracks under heat cycling: The billet aluminum body of the WCF100155 handles thermal expansion and contraction far better than plastic aluminum does not become brittle with age the way nylon-based fittings do.
• O-ring seal degradation: The factory fitting relies on a single-point seal. The WCF100155 uses a double O-ring design that provides redundant sealing if one O-ring surface sees a minor contaminant, the second still holds.
• Vibration fatigue: Diesel and heavy-duty gas trucks transmit substantial vibration through the firewall. The billet aluminum construction is significantly more resistant to vibration-induced cracking than OEM plastic.
• Corrosion resistance: A clear anodized finish protects the aluminum body against coolant chemistry and under-hood moisture no bare metal exposure that would accelerate oxidation.
• Direct-fit replacement, no modifications: The WCF100155 uses the factory push-lock wire retainer clip interface. It drops into the same firewall opening as the OEM fitting no drilling, no tapping, no adapters required.
• Replaces two OEM cross-references: The WCF100155 directly replaces GM/AC Delco part number 15032062 and Dorman part number 800-409.

Construction and Specifications

The WCF100155 fitting is machined from solid billet aluminum billet stock on CNC equipment at Wehrli's facility in DeKalb, Illinois. Every dimension is held to machining tolerances not injection-mold tolerances. The 5/8-inch hose barb end accepts the factory heater hose directly; the firewall-side interface uses the OEM-style push-lock connection secured by a wire retainer clip (the same style as the factory fitting). The double O-ring seal is installed at the factory and is ready to drop in. The clear anodized finish is applied after machining and provides a hard, corrosion-resistant surface layer that does not interfere with fitment.

The package ships at 1.0 lb in a 5-inch by 4-inch by 4-inch box. This is a single-fitting replacement if you also need to replace the heater hose, see sibling part WCF100699. If you need replacement O-rings and retainer clip for a previously installed fitting, see WCF207-27.

Compare: WCF100155 Fitting Only vs. WCF100699 Fitting with Hose Kit

Wehrli offers two solutions for the GM heater core firewall fitting failure. Choose the right one for your situation:

Also available: WCF207-27 GM Billet Heater Core Fitting Hardware Kit (retainer clip + two replacement O-rings). Order this if you are reinstalling an existing fitting after servicing the coolant system.

What's Included with WCF100155

• (1) Wehrli CNC machined billet aluminum coolant heater core firewall fitting
• Double O-ring seals installed on the fitting (factory-ready)
• Direct-fit, push-lock wire retainer clip interface no additional hardware required for installation

Note: Heater hose is not included. If your heater hose also needs replacement, order WCF100699 instead.

Fitment 1999-2023 GM Trucks, SUVs, and Vans

The WCF100155 fits a broad range of GM vehicles from 1999 through 2023. The 1999-2000 model years apply to gas-engine trucks only (the Duramax diesel launched in 2001). All Duramax diesel applications (LB7, LLY, LBZ, LMM, LML, L5P) are covered from 2001 through 2023. Confirm your year, make, model, and engine before ordering. Classic and mid-year designations (2004.5, 2007.5, and 2007 Classic) are noted where applicable.

Full Specifications -- Wehrli WCFWCF100155

Warranty, Made in USA, and California Prop 65

The WCF100155 is covered by Wehrli Custom Fabrication's 12-month limited warranty against defects in material and workmanship from the date of original purchase. During the warranty period, Wehrli will repair or replace the fitting at their discretion. The warranty applies to the original purchaser only and is non-transferable. Warranty claims require dated proof of purchase and a return authorization number from Wehrli; contact them at (630) 277-8239 or through wcfab.com. Warranty is void for improper installation, unauthorized modification, or competition use.

Made in USA: The WCFWCF100155 is designed, machined, and finished at Wehrli Custom Fabrication's facility in DeKalb, Illinois.

California Residents -- Proposition 65 Warning: WARNING: This product can expose you to chemicals known to the State of California to cause cancer and reproductive harm. For more information go to www.P65Warnings.ca.gov.

About Wehrli Custom Fabrication (WCFab)

Wehrli Custom Fabrication known in the diesel community as WCFab is an American manufacturer based in DeKalb, Illinois. Founded by Jason Wehrli, WCFab specializes in precision-machined and fabricated performance and replacement parts for GM Duramax diesel trucks and related GM platforms. Every part is designed, machined, and assembled in the USA. WCFab's product line spans intake manifolds, coolant system components, suspension hardware, and a wide range of billet aluminum accessories built to outlast the OEM plastic and stamped-steel parts they replace. The WCFWCF100155 coolant heater core firewall fitting is one of their most widely sold maintenance and upgrade parts a testament to how common the factory plastic fitting failure is across the entire GM truck and SUV lineup.

Frequently Asked Questions

What does the WCF100155 replace?
The WCF100155 directly replaces the factory GM plastic coolant heater core firewall fitting, OEM part number 15032062 (also sold as Dorman 800-409). This fitting is the plastic connector at the firewall that interfaces the heater core hose with the engine cooling circuit. It is a known failure point on GM trucks and SUVs from 1999 through 2023.

Does the WCF100155 fit my 2001-2023 Duramax diesel truck?
Yes. The WCF100155 fits all Duramax diesel-equipped Chevrolet Silverado 2500HD and 3500HD and GMC Sierra 2500 HD and 3500 HD trucks from 2001 through 2023, covering the LB7, LLY, LBZ, LMM, LML, and L5P engine codes. It also fits non-Duramax gas-engine GM trucks, SUVs, and vans see the full fitment table above for all confirmed applications.

Does the WCF100155 fit 1999 and 2000 model year trucks?
Yes, but only for gas-engine applications. The Duramax 6.6L diesel engine was not available until the 2001 model year. For 1999 and 2000 Silverado 1500 and Sierra 1500 trucks with gas V6 or V8 engines, the WCFWCF100155 is confirmed to fit. The 1999-2000 Suburban, Tahoe, Yukon, and Yukon XL with gas V8 engines are also covered.

What is included with the WCF100155?
The WCF100155 ships as a single billet aluminum fitting with double O-ring seals installed. No heater hose is included. If you also need to replace the heater hose, order WCF100699, which includes the fitting plus a preformed 1/2-inch heater hose assembly. If you only need replacement O-rings and retainer clip for a previously installed fitting, order WCF207-27.

Is any welding or cutting required to install the WCFWCF100155?
No. The WCFWCF100155 is a direct-fit replacement using the factory OEM-style push-lock interface and wire retainer clip -- the same connection style as the original plastic fitting. No welding, drilling, cutting, or tapping is required. Basic hand tools are sufficient for most installations.

Does the WCF100155 fit the Cadillac Escalade, Hummer H2, or Chevrolet Avalanche?
Yes. The WCF100155 fits the 2002-2005 Cadillac Escalade (Base, AWD, ESV, EXT), the 2003-2009 Hummer H2, and the 2002-2005 Chevrolet Avalanche 1500 and 2002-2004 Avalanche 2500. It also fits the 2007-2010 Chevrolet Express and GMC Savana vans in 1500, 2500, and 3500 configurations.

Does the WCF100155 fit the Chevrolet Kodiak C4500 or C5500?
Yes. The WCF100155 is confirmed to fit the 2004-2009 Chevrolet Kodiak C4500 and C5500 medium-duty trucks. Verify your specific Kodiak configuration against the fitment table before ordering.

Why does the factory GM plastic fitting fail?
The factory fitting is molded plastic an acceptable choice when new, but one that degrades over time from repeated heat cycling, coolant chemistry exposure, and the vibration inherent in diesel and heavy-duty gas trucks. The plastic becomes brittle, the seal surfaces wear, and cracks develop that allow coolant to weep or leak at the firewall. The WCF100155 replaces the entire plastic body with CNC machined billet aluminum and a double O-ring seal that maintains a positive seal even as components age.

What is the difference between WCF100155 and WCF100699?
The WCF100155 is the fitting alone. The WCF100699 includes the same billet aluminum fitting plus a preformed 1/2-inch heater hose assembly with quick-connect ends. If your heater hose is in serviceable condition, the WCF100155 is the right choice. If the hose is also cracked, soft, or leaking, the WCF100699 kit saves you from sourcing a separate hose.

Is the WCF100155 legal to use in California?
The WCF100155 is a cooling system maintenance part a direct replacement for a failed OEM fitting. It does not affect emissions equipment. California residents should note that this product carries a California Proposition 65 warning for chemicals known to the State of California to cause cancer and reproductive harm; see www.P65Warnings.ca.gov.

Will installing the WCF100155 void my GM factory warranty?
Replacing a failed OEM fitting with a direct-fit equivalent part generally does not void the factory powertrain warranty. Under the federal Magnuson-Moss Warranty Act, a vehicle manufacturer cannot void your warranty simply because you installed an aftermarket part unless they can prove the aftermarket part directly caused the specific failure being claimed. If you have an active factory warranty, consult your dealer for guidance specific to your situation.