FUJI Racing Supercool Low Temperature High Flow Thermostat – Subaru




FUJI Racing Supercool Low Temperature High Flow Thermostat – Subaru


The Fuji Racing Supercool Thermostat has been in testing for most of 2022, now it’s finally ready to release to the public.

With the Fuji Racing Supercool thermostat in place, your engine coolant is allowed to circulate around the engine much earlier. This allows overall engine temperatures to be reduced sooner than would normally occur. Your coolant’s job is to carry heat out of the engine, take it through your radiator, then flow it back into the engine at a reduced temperature to when it left. This entire process is controlled by the thermostat. Having a thermostat open at a lower temperature than OEM allows the coolant to flow through the radiator quicker and longer.

The Fuji Racing Supercool Thermostat operating temperature is 71oC. OEM Subaru opening temps for turbo models are 78oC & naturally aspirated models are 82oC. The Fuji Supercool thermostat also features a larger opening than OEM allowing for more flow through the thermostat. Fuji Supercool 41mm Opening vs OEM Subaru 39mm opening.

Testing was done on a 2005 WRX STi 2.1 stroker. Fuji had a mix of daily driving & full-day track days (over 6,000 miles combined). Coolant temps never went over 95oC on a 30oC summers day and daily driving was no different to an OEM thermostat. Heaters worked as they should, coolant temperatures were stabilized and didn’t fluctuate. It had an OEM standard coolant radiator fitted, OEM cast impeller water pump, Fuji supercool thermostat, front mount intercooler & front mounted oil cooler. The coolant used was standard Millers Alpine antifreeze.



Suitable for the following models:

  • All Subaru EJ Engines
  • All Subaru EZ H6 Engines


  • 71oC Supercool High Flow Thermostat
  • Seal



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