OTTO Excavator Spare Parts Nkr55 4Jb1T Thermostat Seat 8971396030 897139-6030 8-97139603-0 For Isuzu This product by OTTO, the Nkr55 4Jb1T Thermostat Seat with part number 8971396030, is designed for Isuzu engines to help regulate and maintain their optimal operating temperature.