Diagram reference number 10 in the image below:
" Fitment: 1998 TOYOTA COROLLA - 4 door

Application Notes:

Category: Cooling

SubCategory: Thermostat, Gasket, and Housing

Position: General

Part Number: 163210D010


This is a Engine Coolant Thermostat Housing that fits the 1998 TOYOTA COROLLA - 4 door with the 1ZZFE engine. The Engine Coolant Thermostat Housing is designed by TOYOTA to be part of the Cooling-Thermostat, Gasket, and Housing. The Engine Coolant Thermostat Housing has a position on the vehicle of General. The 1998 TOYOTA COROLLA Engine Coolant Thermostat Housing is a factory made TOYOTA OEM part and it comes with a 12 month 12,000 mile warranty (parts only). Do not be fooled by an aftermarket TOYOTA COROLLA Engine Coolant Thermostat Housing! Buy a factory TOYOTA part and receive peace of mind!
This factory part has a part number of 163210D010.