If you are referring to the issue where some of the preheater systems,
when if left on constantly caused moisture evaporated from the hotter
parts of the engine to condense on the cooler parts (such as you
listed) and cause corrosion, well maybe that occurs. The dryers simply
blow dry air thru the crankcase eliminating (theoretically) moisture
from initiating corrosion. I think that many of the articles we read in
aviation publications take a very simplistic approach to research. I
don't think the charge that if you leave a preheater on 24x7 it will
cause corrosion has ever been proven or disproven adequately, as is
also true with many other things we read. For instance, we are
constantly told that water condenses in the oil in the crankcase and
that we need to fly alot to boil it off. Well, I have done my oil
changes for years (close to 40 oil changes by now) and I usually send a
sample off for analysis. I usually drain the oil overnight, and I don't
usually do it after flying but before, since I like to circulate the
fresh oil through the engine, so the oil is cold from sitting up for a
week or two and should have moisture in it according to common wisdom.
However the analysis reports I get back from Blackstone never show any
sign of moisture in the oil! WTH.
But you might be right. I don't know for sure.

Bud


Dave Butler wrote:
wrote:
The 100 watt bulb trick is to merely place a drop cord with a 100 watt
bulb inside the cowl while parked and leave it on 24x7. This was first
suggested as a cheap and easy way to preheat, especially if 2 100 watt
bulbs were used. Simply put plugs or rags or such in the cowl openings,
place a blanket or 2 over the cowl, and while not as good as a good
preheater, did keep the engine at a temp above the desired level.
Aviation Consumer did an article on this in the past. They used the
same trick when they were evaluating the dryers, and found that as with
the preheaters, this trick did not perform as well as the devices
designed for that purpose, but did keep moisture out of the crankcase.
They found that this trick kept the air temp inside the crankcase from
5 to 10 deg above the dew point, so no moisture collected on the engine
internals.

I have to wonder whether the moisture evaporated from the
above-dew-point crankcase distills out on the below-dew-point rocker
arms and valve mechanism.