MSH THERMAL BYPASS VALVE 12-18 JK AUTO

Heat is one of the biggest enemies of automatic transmission longevity, especially in a Jeep Wrangler that regularly tackles steep trails, oversized tires, heavy loads, or extended periods of low-speed driving. The Mishimoto Thermal Bypass Valve Kit for the 2012–2018 Jeep Wrangler JK addresses a key part of the transmission cooling system by improving fluid circulation and giving owners greater control over transmission temperatures.

From the factory, the Wrangler JK's automatic transmission uses a thermostatic bypass valve to regulate fluid flow through the transmission cooler. When the transmission is cold, the valve limits circulation through the cooler to help the fluid reach its intended operating temperature. Once the transmission warms up, the thermostat opens to allow additional cooling. While this arrangement helps prevent overcooling, a malfunctioning factory valve can restrict fluid circulation and contribute to excessive transmission temperatures.

The Mishimoto Thermal Bypass Valve improves upon this arrangement with a higher-flow design and a fully serviceable thermostat. Its included 160°F thermostat maintains the factory opening temperature while allowing greater fluid flow than the original valve. This makes it an appealing upgrade for Jeep owners who want improved cooling system efficiency without eliminating the benefits of temperature-controlled fluid circulation.

For Wranglers operating primarily in consistently hot climates, Mishimoto also includes a removable thermostat bypass. Installing this component removes the thermostat's restriction and lets transmission fluid circulate through the cooler continuously. This configuration can be useful when managing transmission heat is the primary concern, particularly during demanding off-road use. However, continuous cooling is not recommended for cold-weather environments, where transmission fluid needs to reach an appropriate operating temperature for proper performance.

Construction is another significant improvement over the original component. Mishimoto machines the valve body from billet aluminum and incorporates external cooling fins to increase surface area for heat dissipation. The anodized finish helps protect against corrosion, while the removable thermostat provides serviceability that the factory assembly lacks. Instead of replacing the entire valve when changing thermostat configurations, owners can access and replace the internal component.

Installation is designed to be straightforward, with a direct-fit configuration that works with the Wrangler's existing transmission cooling system. Mishimoto estimates the job can be completed in under an hour, making it a practical upgrade for owners addressing cooling concerns or performing preventive maintenance on their automatic transmission. Backed by a Mishimoto Lifetime Warranty, the kit offers a durable, adaptable approach to transmission temperature management.

Kit Includes: One CNC-machined billet aluminum thermal bypass valve, one removable 160°F thermostat, one removable thermostat bypass with installation hardware, and an assembly instruction card.

Technical Specifications: Billet aluminum construction with an anodized finish and integrated cooling fins. Includes a 160°F thermostat that matches the factory opening temperature. Compatible with additional Mishimoto thermostat options for customized temperature control. Designed to increase transmission fluid flow compared with the factory bypass valve.

Important Cooling Note: Mishimoto does not recommend installing the thermostat bypass in cold climates because continuous transmission fluid circulation through the cooler can prevent the transmission from reaching its intended operating temperature. The included 160°F thermostat is the recommended configuration when cold-weather operation is a consideration.

Fitment Note: Designed for 2012–2018 Jeep Wrangler JK and JK Unlimited models equipped with the 5-speed automatic transmission. Not compatible with manual transmission models.