Transmission thermostat bypass for reducing transmission fluid temps and improving flow.
For the ZF 8-speed transmission used in G42, G87, G20, G80, G22, G26, G82, G83, F90, F92, F97, F98, F95, F96, G29, and Supra A90/GR.
This machined plug will convert the transmission cooling to an open loop - always circulating trans fluid to the cooler instead of closing the loop when cold. With this plug the transmission cooling circuit will always be open and flowing. This replaces the spring and plunger mechanism inside the existing thermostat on the side of the transmission and is similar - but simpler - to what BMW Motorsport did with the GT4 race car. This requires no modifications, is very easy to install, and is completely reversible.
Why do we want an open loop? 1. Reliability from simplicity and 2. to better control high temps. The transmission logic in the ZF programming will close the thermostat to manage temps. But in the interest of reliability, simplicity, and cooling we want this thermostat to always be open for track use (or in other high-load scenarios such as towing). The last thing you want is for a thermostat to get stuck closed, be slow to operate, and cause spikes in transmission temp that will shut down your session. And with full flow the fluid is constantly circulating, getting more even cooling and avoiding heat soak.
WARM-UP NOTE: because cold fluid does not flow as well as warm, this piece is not recommended for cars that are driven in near-freezing temperatures. In this case the factory logic makes sense - close the thermostat to get the fluid up to temp sooner. Also with this piece you will need to let the transmission reach a minimum temp before driving (> 20°C / 68°F). A few minutes of idling should be sufficient.
