If you plan on tracking your car and want to reduce the amount fluid you are loosing in the overflow you can simply add a 1.3 bar radiator cap.

The STI Radiator Cap increases the terminal pressure inside (From 1.0 bar to 1.3 bar) your cooling system. This increases the maximum operating temperature capability of your vehicle's cooling system. This will help prevent coolant loss due to boil-over under extreme operating conditions, which became a problem with the smaller Process West FMIC overflow bottle.

DO NOT CHANGE YOUR CAP IF YOUR VEHICLE HAS BEEN IN USE WITHIN THE LAST 30 MINUTES

Have a rag handy, apart from that no tools required.

There are other brand radiator caps out there such as Blitz, Apexi, etc but we are sticking with the family's STi radiator cap.

Removing ye old OEM raditaor cap may require some persuasion. Be sure to have a backup near by.

Here is a comparison of the STi (left) and the OEM (right). See the difference? Well if you do could you please let me know as I could not.

Installing the STi cap required even more muscle power. So you might want to call in some help.

STi Part Number ST4511355000, Fits the following models: 2002-2005 2.5RS/TS, 2002-2006 WRX, 2006 2.5i Impreza.