One of the common weak points of both the 4G63 & the 4B11 is the rise of oil temperature. It is seen more often during hard driving at closed tracks and other events. The EVO uses a thermo switch that will activate when the temperature gets around 85 deg C. Yet when the oil temperature is low, it won’t activate thus restricting oil flow to the oil cooler which then consequently raises the oil temperature to unwanted levels. This Tomei oil thermo killer allows oil to flow into the oil cooler constantly regardless of the oils temperature. It is still easy to revert back to the stock thermo switch during winter periods to prevent over cooling as well.