WC Fab Transmission Cooler Thermostat Bypass Plug, 2017-2019 L5P

Part# WCF100469


WARNING: Cancer and Reproductive Harm - www.P65Warnings.Ca.Gov

Fits: 2017 thru 2019 Chevy Silverado/GMC Sierra 2500/3500HD L5P Duramax Diesel

The stock thermostatic bypass for warming up the Allison transmission quickly in cold weather conditions is a good idea in principle, but in practice we've seen the valve fail forcing trans fluid around the cooler in warm weather conditions that causes dangerous fluid temperatures for built and stock transmissions alike. This design has been run on Wehrli Custom Fabrication's shop development trucks and with built transmissions successfully. 


  • CNC Machined Billet Aluminum Thermostatic Bypass Plug
  • Black Anodized Finish
  • High temperature silicone O-ring seals
  • Great for stock or built transmissions towing heavy in warm climates
  • Reduces fluid flow restriction to trans cooler
  • Experience fluid temperature drops from 15-50 degrees F
  • Direct replacement of the failure prone OEM thermostat
  • Simple installation, easily swap back to OEM setup for cold weather use


  • Thermostatic bypass plug
  • O-Ring seals