Fasthotrod
Well-known member
Speaking with technical the best I could get was that the alternator does not like to sit in the same spot for extended periods -- spinning it a few times keeps it clean.
Typically, it's to prevent flat spots on the bearings and help keep moisture from condensing inside the windings.
Why does an engine need to run every week ?
A couple of reasons... one is to maintain a thin layer of oil on the engine components. When an engine sits, it's subject to ambient heating/cooling effects and when those temps drop down low enough, water will condense from the air and cling to the metal surfaces. You see this on your car in the morning, and sometimes on your cold beer can on a humid day.

...which leads to another reason to run the engine. That water mixes with the oil in the crankcase, and develops an acid that can eat at the metal in the engine. Running the engine up to temps that can burn off the moisture in the engine helps eliminate this. This is one reason why larger industrial engines have oil pan heaters and immersion heaters, to keep the engine above the dew point so moisture doesn't condense in the engine.
Hope this helps.
Mark
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