The 6R80 Transmission uses an internal Thermal Bypass Valve that functions much like a thermostat in your engine’s cooling system. On startup, the valve remains closed, limiting fluid flow through the auxiliary transmission cooler — helping the trans warm up quickly. Once the optimal temperature is reached, the valve opens, allowing fluid to pass through the cooler before re-entering the transmission.

Here’s why this matters for your build:
This bypass valve is standard on 2011–2014 F150s and Mustangs, and also found in 2015–2017 Mustangs. However, 2015–2017 F150 6R80s use an external bypass cooler unit instead — which is usually removed in engine swaps.

If you’re using a Gen 2 F150 transmission (commonly sourced for Coyote swaps or performance builds), installing this internal bypass valve is essential to maintaining proper temperature regulation and fluid routing. Without it, your transmission may not function as intended — especially under performance use.

Why it’s important:

  • Ensures correct fluid flow and warm-up behavior in swap applications

  • Replaces the missing external bypass found in 15–17 F150s

  • Vital for Gen 2 6R80 transmissions used in performance or custom builds

  • Helps prevent overheating and inconsistent fluid pressure

Recommended For:

  • Gen 2 F150 6R80 users (2015–2017) in Coyote swaps

  • Any high-performance or transmission-only swap using a Gen 2 core

  • Builders who have removed the OEM external bypass unit

Works on all 2015-2017 Mustang 6R80 transmissions