The 1966 Mustang has a fixed blade fan, attached directly to the pulley that turns the water pump. These fans are noisy, think of it as an airplane prop out in front of your engine. The faster it turns the louder it gets. Coincidentally, this is the opposite of what is needed for cooling. The fan is most critical when the car is stopped, and there is no air being naturally forced over the radiator to cool the engine. At speed, when the engine is running at higer RPMs the air from the car rolling down the road pushes over the radiator and cools it nicely.
Old fixed blade fan
Over the years, there have been a number of improvements to cooling methods. There have been slip clutches on the fan shaft so that it will start to slip at higher RPMs and reduce noise. There have been flex blades, fan blades that flatten out and don't slap as much air at higher RPMs. By far, the best improvement has been the electric fan. Electric fans are controlled by a thermostat sensor attached to the water pump. When the temperature of the coolant hits the upper limit, the thermostat kicks on an electric fan until the temperature drops below the lower limit. It is significantly quieter, and more efficient since it is only running when it is required.
It took a bit of juggling, since the new fan was just a hair thicker than the space we had between the engine and the radiator. We ended up placing the fan in front of the radiator, and setting it up in "pusher" mode. This has the side effect of making the engine compartment just a hair cleaner.
Electric fan in place, in front of radiator
We wired up the sensor and fan relay and were ready to test out the new upgrade.
