My assumption is that the airflow was originally channeled through the
radiator because the radiator support bulkhead had only one opening, for
the radiator, and the air went on through it. Having passed through, it
could be pulled through the fan or could flow around the fan, depending
on road and air speed. Now that there is a fan in front of the radiator,
the airflow is restricted at 70mph unless the fan is on. Chances are that
the electric fan has more efficient larger fan blades than the original,
which makes the resistance problem worse, though the fan performance
better. As an example of the air resistance to flowing through and by an
object, observe the way water flows around a rock in a flowing stream.
Notice how it sort of piles up on the upstream side. That air pile-up is,
I think, why the car needs the fan at 70 mph.
Bob
On Fri, 18 Jul 1997 11:53:33 -0500 "Thomas James Pokrefke, III"
<pokrefke@ocean.st.usm.edu> writes:
>I replaced the engine-driven cooling fan on the 'B with an electric
>version. There is only about 2" of room behind the radiator, so I had
>to mount the fan in front (pushing air through the radiator).
>
>I would have thought that @ 70 mph, there would be enough air moving
>across the radiator to keep the engine cool. If the fan is off, the
>temp guage rides halfway between 'N'ormal and 'H'ot. With the fan on,
>it rides right at 'N'ormal.
>
>Anyone want to guess why?
>
>FWIW - I have a dash mounted switch that turns the fan on/off.
>
>
>Thomas James Pokrefke, III
>1970 MGB
>pokrefke@ocean.st.usm.edu
>http://ocean.st.usm.edu/~pokrefke
>
>
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