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Wiring Diagram for Datsun 510 (68-72) cooling system using electric fan upgrade for two speed fan control - PAGE-2.

The goals of the lower voltage, two speed fan control design is to reduce both the electrical power demand for average street use and also reduce fan noise.  By starting fan at lower temperature with lower speed, it smooths out system temperature peaks and reduces overall load.  If run live after turn-off, this also saves battery capacity for restart.

Component design descriptions for proven as-built system with usage details.  Design for stock L16, L18, or L20B engines,  Likely a great upgrade for other engine swaps such as SR20, KA24, etc.  The devil is in the design details.  The circuit set up for a single fan but can be easily adapted for dual fan system.

Fans suggested are oriented toward low power consumption, low profile, and lower noise and well suited for as-designed design radiator.  Higher CFM versions are applicable with double the amperage requirement, taller profiles (less engine room) and nearly double the flow rates.  As noted, fan choice dependent on engine build, driving style, local climate, and alternator capacity (harness suitability).

Engine cooling system design requires consideration of coolant operating temperature (thermostat), radiator efficiency with available heat disposal capacity per given installation, fan switch temperature ratings coincident with placement within radiator, engine size, fan flow capacity, etc.