This discussion of radiator fans has been interesting. One thing to
keep in mind is the difference between what it does and why it does
it, or more to the point, why the engineers did it that way.
Sure, many cars today spin their fans after being shut off, even
cycling on/off a few times as the radiator sensor cools, then warms,
then cools. That cycling may be from the water flowing inside the
radiator due to temperature differences (i.e. thermal convection).
It isn't obvious whether much water is flowing between the radiator
and the block. At some temperature the thermostat should shut off
the flow between them. Maybe that's when the fan stops for good. A
temp gauges should show a rise after the engine is shut off (if the
gauge is still powered) because heat still propagates from inside the
engine to the fringe of the head where the sensor is attached.
The real question isn't what a particular car does but whether it was
intentionally engineered to do it for some specific reason. It might
be that they implemented some specific heat-management technique for
post-shutdown, and that may have included thermal convection between
radiator and block. Or it may be that they were concerned about
electronics or turbo bearings, or some other thing. Or as Dave
Massey pointed out, it might just be that the designers saved a few
bucks on a relay and lower-current ignition switch, and judged the
result acceptable. Just because the fan stays on post-shutdown
doesn't mean it was the engineers' primary intent.
It is a safe bet that few of those specific-engineering reasons
applied to TR's except possibly keeping fuel lines and carbs cool and
saving bucks. If you want to wire your new electric fans that way,
go ahead. The pros and cons are obvious. But it isn't required. (I
never saw a mechanical fan that would spin for long after the engine
was shut off. :-)
Louvers are the ultimate answer, you know. They look cool, require
minimal tooling, don't run down the battery, don't need no Lucas
connectors...
Jim Muller
jimmuller@rcn.com
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