In Line Thermostat Switch (For Oil Cooler Electric Fan)

This in-line thermostat switch is designed to automatically control electric cooling fans fitted to aftermarket Mesa-style oil coolers, switching them on and off at a preset temperature of 185°F (85°C). By activating the fan only when needed, this thermostat helps maintain stable oil temperatures, prevents overheating during heavy driving or hot weather, and reduces unnecessary electrical load when the engine is running cool.

The switch can be installed in two ways—either screwed directly into the inlet of the oil cooler using the built-in 8AN thread, or mounted in-line on the oil hose using the supplied 1/2″ (13mm) barbed fittings. This makes it ideal for both custom installations and retrofits on air-cooled VW engines running remote oil coolers. The compact design ensures minimal flow restriction, and the durable construction withstands high oil temperatures and pressure variations commonly experienced in performance or long-distance engines.

Electrical wiring is straightforward:
• Lead 1 wires directly to the fan.
• Lead 2 connects to a relay that supplies switched power.
Once the oil temperature reaches 185°F, the switch activates the fan; when temperatures drop below the threshold, it automatically switches the fan off again. This helps keep oil within its optimal range while maintaining engine reliability—especially important for tuned engines, off-road vehicles, and air-cooled setups working under load.

A simple, effective and essential component for any aftermarket oil-cooling system that requires automated fan control.