Wehrli Fabrication WCF100025 Duramax Coolant Plug

The WCF100025 Wehrli Custom Fabrication Duramax Coolant Plug is a billet aluminum, black anodized replacement coolant plug designed to fit the 1.1" bore engine cover coolant port found on 2001-2016 Chevrolet Silverado 2500/3500HD and GMC Sierra 2500/3500HD trucks equipped with the 6.6L LB7, LLY, LBZ, LMM, or LML Duramax diesel engine. WCF100025 provides a precision press-fit seal secured with a high temperature silicone O-ring and a 13mm bolt, eliminating coolant seepage from the engine cover port. Made in the USA in DeKalb, Illinois by Wehrli Custom Fabrication (WCFab), part number WCF100025 is built to last the life of your Duramax with zero compromise on fit or finish.

Why WCF100025 Outperforms Stock Coolant Plugging Approaches

The factory engine cover coolant port on the 6.6L Duramax was originally designed for a heater core or auxiliary coolant circuit connection. When that port is unused or a heater core delete is performed, many owners resort to generic rubber caps or improvised plugs that degrade under sustained heat cycles and coolant chemistry. WCF100025 addresses every weakness of those approaches:

• Billet precision: Machined from aircraft-grade billet aluminum to match the exact 1.1" bore diameter, WCF100025 seats flush without gaps or wobble that plague generic plugs.
• High temperature O-ring seal: The included silicone O-ring is rated for sustained high-heat environments, resisting the temperature swings common in diesel cooling systems far better than standard rubber.
• Mechanical retention: Unlike a threaded plug that relies solely on thread engagement, WCF100025 uses a press-fit body retained by a 13mm bolt, distributing clamping load evenly and eliminating the risk of cross-threading or galling in the aluminum engine cover.
• Corrosion resistance: The black anodized finish creates a hard oxide layer that resists coolant chemistry, road salts, and underhood moisture for long-term durability.
• Made in the USA: Every WCF100025 plug is manufactured in Wehrli's DeKalb, Illinois facility, ensuring consistent quality control from raw material to finished part.

Material and Construction

WCF100025 starts as a solid billet aluminum bar stock, CNC-machined to hold tight tolerances across the 1.1" plug body diameter. The external surface receives a Type II black anodize treatment that bonds to the aluminum at the molecular level, providing a finish that will not chip, peel, or flake under underhood conditions. The plug body is engineered for a push-fit installation into the engine cover coolant port; a groove machined into the plug body seats the included high temperature silicone O-ring, which compresses evenly during installation to create a leak-free radial seal. A 13mm bolt through the plug face locks the assembly in place so vibration from the diesel powertrain cannot work the plug loose over time. No thread taps, no sealants, and no special tools are required beyond a standard 13mm socket.

Fitment

What's Included

• (1) Billet aluminum black anodized coolant plug, 1.1" bore (WCFWCF100025)
• (1) High temperature silicone O-ring seal

Full Specifications

Related Wehrli Custom Fabrication Products

• WCF100155 - GM Billet Coolant Heater Core Firewall Fitting: A billet aluminum replacement fitting for the heater core firewall coolant ports, pairs with WCFWCF100025 for a complete heater core delete on your Duramax.
• WCF100252 - 2011-2016 LML Duramax Coolant Bypass Kit with Plug: A complete coolant bypass solution for LML Duramax trucks that includes a plug, designed to work alongside the same port that WCFWCF100025 seals.

Frequently Asked Questions

What is WCF100025 used for?
WCF100025 is a billet aluminum coolant plug that seals the 1.1" bore engine cover coolant port on 2001-2016 6.6L Duramax diesel engines. It is commonly used during heater core deletes or when the factory port is left unused after a cooling system modification.

What Duramax engines and years does WCF100025 fit?
WCF100025 fits 2001-2016 Chevrolet Silverado 2500/3500HD and GMC Sierra 2500/3500HD trucks equipped with the 6.6L LB7 (2001-2004), LLY (2004-2005), LBZ (2006-2007), LMM (2007-2010), and LML (2011-2016) Duramax diesel engines. See the fitment table above for all individual year and model combinations.

Does WCF100025 require any special tools to install?
No special tools are required. Installation involves pressing the plug body into the engine cover coolant port by hand and tightening the 13mm retention bolt with a standard socket. No thread taps, sealants, or machining are needed.

Is WCF100025 a threaded plug?
No. WCF100025 uses a press-fit (push-fit) design rather than a threaded interface. The plug body seats into the bore and is held in place by a 13mm bolt, which distributes clamping load evenly and eliminates cross-threading risk in the aluminum engine cover.

What O-ring is included with WCF100025?
A high temperature silicone O-ring is included with every WCF100025. Silicone is chosen specifically for its resistance to the sustained heat cycles and coolant chemistry found in diesel cooling systems, providing a more durable seal than standard rubber O-rings.

Where is WCF100025 manufactured?
WCF100025 is Made in the USA. It is designed, machined, and finished at the Wehrli Custom Fabrication facility in DeKalb, Illinois.

What is the warranty on WCF100025?
Wehrli Custom Fabrication warrants WCF100025 for 12 months from the date of purchase against defects in material and workmanship. The warranty is non-transferable. Contact Wehrli directly to obtain a Return Authorization (RA) number before sending any part back.

Can I use WCF100025 on a 3500HD Duramax truck?
Yes. WCF100025 fits both 2500 and 3500HD variants of the Chevrolet Silverado and GMC Sierra for all applicable model years (2001-2016) and engine codes (LB7, LLY, LBZ, LMM, LML). All 3500HD fitments are listed individually in the fitment table above.

Does WCF100025 work for a heater core delete on a Duramax?
Yes. WCF100025 is a direct solution for plugging the engine cover coolant port during a heater core delete. For a complete heater core delete, you may also want to look at WCF100155 (GM Billet Coolant Heater Core Firewall Fitting) or, for 2011-2016 LML trucks, the WCF100252 Coolant Bypass Kit with Plug.

Will the black anodized finish on WCF100025 hold up under the hood?
Yes. The black anodized finish on WCF100025 is a Type II hard anodize that bonds at the molecular level with the aluminum, creating a corrosion-resistant layer that withstands underhood heat, coolant exposure, and road salt without chipping or peeling.

California Proposition 65 Warning

WARNING: This product can expose you to chemicals including lead and lead compounds, which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information, go to www.P65Warnings.ca.gov.