This fact about car and truck generators is not known to most. We hope, you find this of interest.
Both ends of most generators after the mid 1930’s had openings for air to pass through their internal moving parts. The small fan on the front it is attached to a pulley that is turned by the belt reaching the harmonic balancer of the engine.
The air is moved in reverse that one might think. It is pulled from the back of the engine compartment to the front. Why?
The air is first drawn over the rear brushes that rub the smooth surface of the armature. Here, more heat is developed.
During heavy rain some water could be pulled through the large radiator by the engine fan. It does not enter the nearby generator because the small fan forces air from the rear and out the front!
From the mid 1930’s and older there is rarely openings in the generator ends and a cooling fan does not exist. Most side roads were gravel or dirt. Fine dust could be pulled into the internals of the generator and shorten the time between rebuilding. Thus, the generator was sealed. Yes, the internals run hotter but it was the better of two evils.
In later years, most roads became paved, lessening much dust. There is one exception that continued to use sealed generators. Farm tractors worked regularly in the dusty fields during planting and especially at harvest time. Thus, the generator is sealed and runs much warmer that most cars and trucks.
