Thermal Bypass Valves 101 – What are they and How do they Work

The automatic transmission in your vehicle is practically the defining feature of the vehicle. The sturdy gear sets housed inside, transferring power from the engine, are the gatekeeper to hauling heavy payloads, traversing treacherous rock gardens, or setting blistering lap times. No matter how powerful your engine is, without the transmission, your vehicle is dead weight. 

Where the transmission is the soul of your car, truck, or Jeep, keeping it cool can sometimes pose a challenge. True, there are many ways to maintain transmission fluid temperatures, but they won’t do you any good if the fluid never makes it to the cooler. That’s why a sturdy thermal bypass valve is essential for any automatic shifting performance vehicle.

What is a thermal bypass valve? I’m glad you asked! To understand the thermal bypass valve’s purpose, we need to dive further into the bell housing. The automatic transmission is a collection of planetary gear sets, clutch packs, shafts, and other wizardry suspended in a slurry of automatic transmission fluid, or ATF. This fluid acts as a lubricant for the hundreds of moving parts inside of the transmission. It’s also instrumental in the torque converter’s operation, working as a fluid clutch to get your machine moving from a complete stop. Like most lubricants, ATF works best once it reaches a prime operating temperature range. Too cold, and the fluid is more viscous, meaning the entire vehicle needs to work harder. Too hot, and the fluid thins out too much and can even burn, resulting in irreparable damage to the transmission components. 

The thermal bypass valve is the gatekeeper of cooling your transmission, quite literally. Depending on the vehicle, ATF will cycle out through an external cooler once it reaches a specified temperature. Once that heat builds, an internal thermostat shifts and opens a passageway to the cooler. In essence, it’s a thermostat for your automatic transmission fluid.

In theory, the thermal bypass valve is instrumental in peak transmission performance. In practice, however, this valve can malfunction, resulting in the automotive equivalent of a heart attack. The thermostat can stick closed, causing overheating in the transmission fluid, and in some cases, damaging the transmission.

We here at Mishimoto want to ensure your transmission’s safety. So, in addition to the plethora of universal and direct fit transmission cooler kits we offer, we’re giving a wide selection of thermal bypass valves an overhaul. 

All of our valves start with a sleek and sturdy billet aluminum housing, anodized in black to fit the look of any build. Not only does the black anodizing add some flair, but the billet aluminum construction is sure to stand up to anything you can throw at it. The beauty is more than just skin deep as well. All of our bypass valves include a hearty thermostat that matches factory specifications for dependable performance from your transmission. Our design allows for more cooling options as well. This thermostat is easily swapped with alternate thermostat temperatures, depending on the climate. We also include a full-flow pin or full-flow designs for those in hotter climates or putting the transmission under heavy load, eliminating the thermostat and allowing constant flow to the external transmission cooler.

This particular thermal bypass valve is designed for JK Wranglers, but our valves come in plenty of shapes and sizes.

From the job site to the drag strip, maintaining your vehicle’s automatic transmission fluid temperature is vital. Whether you’re looking for a more dependable thermostat, or you’re in a hot climate and need permanent flow to the external cooler, our Thermal Bypass Valves offers a range of flexibility and dependability for your vehicle’s transmission. 

Mishimoto Thermal Bypass Valves

Thanks for Reading!

-Nick

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