Exmark OEM Part 1643163
Used as a temporary holding for coolant that expands when hot to prevent leaking. As the coolant cools, the vacuum pulls the fluid back into the radiator to ensure the system remains full
Used on several Toro and Exmark models including but not limited to:
Toro Z Master, Toro Dingo TX550, TX525, TX700, TX1000 & TX1300
Exmark Lazer Z liquid cooled & diesel,