17-19 L5P Duramax / 14-18 GM 1500 Transmission Cooler Thermostat Bypass Plug

Keep transmission temps in check

The factory transmission cooler thermostat can fail and send fluid around the cooler, which in warm weather leads to dangerous fluid temperatures for stock and built transmissions.

This CNC-machined billet plug replaces the thermostat and cuts flow restriction to the cooler; Wehrli says fluid temperatures drop 15-50°F. High-temperature silicone O-rings seal it, it installs quickly, and you can go back to the factory setup for cold weather. Wehrli recommends it for heavy towing in warm climates.

Who it's for

2017-2019 L5P owners who tow heavy in warm weather, with stock or built transmissions.

Key specs (per Wehrli)

What's included

• Thermostat bypass plug with O-rings

Fitment notes

• Fits 2017-2019 Chevrolet Silverado / GMC Sierra 2500 HD and 3500 HD with the 6.6L L5P Duramax.
• For vehicles with a factory transmission cooler thermostat bypass (6L80, 6L90, 8L90).
• Wehrli says it also fits 2014-2018 Silverado / Sierra 1500, 2015-2020 Suburban, Tahoe and Yukon, and the 2015 Escalade with gas engines; we list it for the diesel HD trucks only.

Professional install available at Powertech Diesel, Idaho Falls — call 208-542-7793.