RCM Low Temperature Thermostat (Subaru)

The Roger Clark Motorsport  thermostat is designed not only to improve reliability (thanks to its superior construction and RCM's strict quality control inspection process) but also to provide an earlier start in your engine's cooling process.

With a low temp thermostat in place your engine coolant is allowed to circulate around the engine much earlier which allows overall engine temperatures to be reduced sooner than they would normally occur. Ultimately your coolants job is to carry heat out of the engine, take it through your radiator (where the actual temperature reduction will occur) and then flow back into the engine at a reduced temperature to when it left. This entire process is activated by a door opening and closing (your thermostat), so if this "door" is opened earlier than would normally be expected then the coolant can get a head start on taking heat out of the engine.

With coolant flowing through your engine at an earlier stage (thanks to a low temp thermostat) the next area to make significant temperature drops would be a performance radiator. A larger radiator not only increases how much coolant can be present within it at any one time, but with a larger surface area and an improved fin design this can allow a higher volume of air to pass through, this in turn lowers temperatures on your coolant fluid faster, more efficiently and in greater volume.

Low temperature thermostats are most suited for vehicles driven "spiritdley" on either road or track where engine temperatures are likely to raise at a much faster rate than if the engine was being driven under normal road use.

If your car is only driven on the street, and is not being used in high temperature environments, then the OEM thermostat will be more ideal because it will keep the car in normal operating temperatures in those normal operating conditions.  A cooler thermostat that opens earlier will keep the car running cooler, but that can lead to the car throwing a code for that same reason.