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Subaru Thermostat heads up

Brett Proctor

Well-known member
Not sure what years of Subaru engines this will cover but for mine (1998 EJ25D ) The thermostat will not open unless the heater line circulates water back to the engine even if the heater isn't working.
In my case I had to install a "H" fitting in the line so water would circulate back to the engine.
If this is not done the thermostat will not open and the engine WILL overheat.
I removed the thermostat till I got the "H" fitting made so the water pump would circulate water through the block.

Just a heads up