Jim,
You ask about a flex-a-lite fan - Flex-A-Lite is a brand name. The 2 types of add on fans are an electric fan and a flex fan.
Electric fan - a fan, powered by an electric motor, can push or pull air. If used as a replacement to the engine driven fan, you might a slight HP improvement. Can also be used as an auxillary fan, in addition to the factory fan.
Flex fan - a fan, fixed to the water pump (no viscous or thermal coupling), spins at engine speed. At high RPM, blades will flex to almost flat, reducing both their resistance through the air as well as volume of air moved (basically zero). This is great at high vehicle speeds, as moving vehicle moves air through radiator. However, when the fan flexes at high engine speeds, and you are rock crawling, you have a greater chance of overheating, since the vehicle speed is not moving air through the radiator.
Hope this makes sense.
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Scott
1993 Ranger, Modified
sjbosso@mindspring.com