2002-2005 WRX. 2006-2007 WRX. 2008-2014 WRX. 2004-2007 STi. 2008-2014 STi. 2015-2021 STi. By increasing the boiling point, you decrease the amount of air bubbles that form in the coolant. Air is less effective at removing heat from the engine than coolant, so by reducing the air in your system, your coolant can more efficiently cool your engine.
