Gates 33857S Engine Coolant Thermostat

Gates Premium Thermostat for Subaru Cooling Control

The Gates Premium Thermostat 33857S is a 170-degree engine coolant thermostat built for Subaru cooling systems that need stable temperature regulation. It uses stainless steel and copper construction for improved corrosion resistance and an upgraded spring to help maintain consistent opening performance during normal operation.

Key Features

• 170-degree start-to-open temperature for Subaru applications that call for alternate-temperature cooling control
• Heavy-gauge stainless steel and copper construction for corrosion resistance
• Reverse poppet design for proper coolant flow control
• Upgraded spring for improved temperature stability under normal operation
• Premium thermostat design from Gates
• Part number 33857S for direct catalog identification

Product Details

This Gates Premium Thermostat 33857S is built for drivers servicing Subaru WRX STI, WRX, Legacy, Outback, Impreza, Forester, and Baja cooling systems across a wide range of model years. It is a direct-fit engine coolant thermostat for applications that specify a 170-degree opening point, including 2020-2021 Subaru WRX STI, 2013-2018 Subaru WRX STI, 2015-2019 Subaru Legacy, 1990-2009 Subaru Legacy, 2019 Subaru Outback, 2015-2017 Subaru Outback, 2000-2009 Subaru Outback, 2012-2016 Subaru WRX, 1993-2014 Subaru Impreza, 1998-2013 Subaru Forester, and 2003-2006 Subaru Baja. This part cross-references Beck/Arnley 143-0710 and Motorad 294-170 for the same application.

Common Cooling System Issues It Can Address

• Engine running too cool or taking too long to reach operating temperature
• Temperature fluctuation caused by a worn thermostat spring
• Corrosion-related thermostat sticking in Subaru cooling systems
• Inconsistent coolant flow control during normal driving
• Replacement needs during cooling system service on WRX STI, WRX, Legacy, Outback, Impreza, Forester, or Baja models

Installation Notes and Tips

Verify the 170-degree specification against the vehicle’s original thermostat before installation. Inspect the thermostat housing, sealing surfaces, and coolant condition during service, and replace any damaged components before reassembly. Confirm fitment by year, make, and model, since Subaru applications in this range may use different cooling calibrations.

Quality Assurance

Gates Premium Thermostats are built with corrosion-resistant materials and an upgraded spring to support stable temperature control in normal operation. The 33857S is engineered as a premium replacement thermostat for Subaru cooling system service.