Why Use an Oil Thermostat?. Every single Improved Racing thermostat undergoes rigurous inspection, functional testing, and certification before it leaves our doors. The FSM thermostat features female -10AN O-ring boss threads and is available with optional fittings in 3/8" or 1/2" hose barb or AN fittings in -6AN, -8AN, -10AN, or -12AN.
