Mishimoto Thermal Bypass Valve Kit, Jeep Wrangler JK 2012-2018

On the 2012-2018 Jeep Wrangler JK, a small thermostatic bypass valve sits in the transmission cooler lines. From the factory it holds fluid back from the cooler until the transmission warms up, which is fine when it works. The problem is the thermostat inside this valve is a known failure point: when it sticks closed it stops fluid from ever reaching the cooler, and the transmission cooks itself. If your JK is climbing into the 230s and 240s on the trans temp gauge and the fluid still looks good, this valve is the usual suspect.

This is Mishimoto's direct-fit replacement (part MMTC-JK-TBV), machined from billet aluminum and anodized black. Unlike the sealed factory unit, the thermostat is fully serviceable and removable. The included thermostat opens at the stock 160F (71C) so cold-climate warm-up behavior stays correct, or you can drop in the supplied bypass insert instead for constant full flow to the cooler year round, which is what most people in hot states want. Either way it flows more than the restrictive stock valve, so the cooler you already have actually does its job.

Fitment is a bolt-in on the 3.6L Pentastar JK and JKU running the factory 42RLE or W5A580 transmission. It threads into the same cooler lines as the OEM valve, so it comes off with a wrench and a crescent to hold the housing, no cutting or adapters. In the box you get the CNC billet valve, the removable thermostat, the removable bypass with install hardware, and an assembly card. Backed by the Mishimoto lifetime warranty. Ships from the USA, handling in 1-2 business days.