Wehrli WCF100469 Billet Trans Cooler Thermostat Bypass Plug for 2017-2019 L5P

Vehicle Fitment

• 2017-2019 Chevrolet Silverado 2500 HD / 3500 HD (6.6L Duramax L5P, Allison 6L80 / 6L90 / 8L90)
• 2017-2019 GMC Sierra 2500 HD / 3500 HD (6.6L Duramax L5P, Allison 6L80 / 6L90 / 8L90)
• 2014-2018 Chevrolet Silverado 1500 / GMC Sierra 1500 (4.3L, 5.3L, 6.2L - with factory trans cooler thermostat bypass)
• 2015-2020 Chevrolet Suburban / Tahoe / GMC Yukon (5.3L, 6.2L - with factory trans cooler thermostat bypass)
• 2015 Cadillac Escalade (6.2L - with factory trans cooler thermostat bypass)

Fitment Notes

• Only compatible with vehicles equipped with a factory-installed transmission cooler thermostat bypass (6L80, 6L90, or 8L90 transmissions)
• Recommended for trucks with stock or built transmissions performing heavy towing in warm climates
• Can be swapped back to the OEM thermostat for cold weather use - reversible installation
• Not recommended as a permanent solution in extreme cold weather environments where rapid transmission warm-up is critical

Features

• Reduces transmission fluid temperature by 15-50°F by eliminating flow restriction to the trans cooler
• Replaces the failure-prone OEM thermostatic bypass valve that can lock open in warm weather and cause dangerously high fluid temperatures
• CNC machined billet aluminum construction for long-term durability and heat resistance
• High-temperature silicone O-ring seals ensure a leak-free, secure fit
• Black anodized finish for corrosion resistance
• Simple installation - reversible for cold weather OEM swap-back
• Made in the USA by Wehrli Custom Fabrication

Specifications

• Material: CNC Machined Billet Aluminum
• Finish: Black Anodized
• Seals: High-Temperature Silicone O-Rings (included)
• Transmission Compatibility: Allison 6L80, 6L90, 8L90
• Fluid Temperature Reduction: 15-50°F vs. stock
• Weight: 1.0 lb
• Package Dimensions: 11" (W) x 9" (L) x 1" (H)
• Warranty: 12 Months

Included Components

• 1x Wehrli Billet Aluminum Transmission Cooler Thermostat Bypass Plug - Black Anodized
• 1x High-Temperature Silicone O-Ring Set

Product Description

The Wehrli Custom Fabrication WCF100469 is a CNC machined billet aluminum transmission cooler thermostat bypass plug designed as a direct replacement for the failure-prone OEM thermostatic bypass valve on 2017-2019 GM L5P Duramax trucks and compatible GM 1500 and SUV platforms equipped with Allison 6L80, 6L90, or 8L90 transmissions. The factory valve is designed to warm the Allison transmission quickly in cold weather by temporarily routing fluid around the cooler - a sound concept in principle. However, the OEM valve is known to fail in the open position, forcing trans fluid around the cooler even in warm weather conditions and causing dangerously elevated fluid temperatures in both stock and built transmissions. This bypass plug permanently routes fluid through the cooler at all times, dropping operating temperatures by 15-50°F.

Sealed with high-temperature silicone O-rings and finished in black anodize, the WCF100469 installs quickly with simple hand tools and is fully reversible - the OEM thermostat can be reinstalled for extended cold weather use if needed. Validated on WCFab's own shop development trucks and built transmission applications, this plug is particularly recommended for trucks performing heavy towing in warm climates where keeping transmission fluid temperatures in check is critical to long-term drivetrain reliability.