[Vwdiesel] block heater in freeze plug

[Val Christian]

This was used to eliminate carburator icing, which can happen when
moist air is cooled in a carburator.  It also requires that the engine
be running, to create the heat off the exhaust.  I think the objective
here is to pre-heat the engine, prior to start.

It might be useful to discuss why we're interested in pre-heating the
engine.

On aircraft piston engines, preheating is done primarily to get the
cylinders warm.  This aids in starting, but also keeps gasoline from
condensing on the cylinder walls.  When this happens, oil is washed
off the cylinder wall.  Secondary effects include reduction of engine
life, due to poor lubrication when the cylinder walls are washed at
startup.

On diesel engines, such as ours, it is often argued that preheating the
oil, causes it to flow better at startup, reducing startup wear.  Reducing
cavitation at the oil pump in extreme cold weather is another good reason.
Probably not a factor at 40F, but definitely a concern at -20F.

Probably the foremost reason for preheating is to present a better
environment for cold starting.  Face it, if we can ease starting problems
that may exist with an older engine only a couple of weeks out of the year,
it'll extend our practical engine life.  Having warm cylinders, which
result in higher compression temperatures, makes starting much easier.
In this case, heating the coolant is the way to warm the cylinders.
Heating the oil, while it may help flow, doesn't really heat the cylinders
much.  Besides, flow problems and cavitation problems can be fixed with
different oils.

[nb: I have been faced with very thick oil, in extreme cold, where the
starter, while turning the engine OK, didn't quite turn it fast enough for
starting.  One of those old Rabbits with 300K or so.  A propane torch,
evenly swept across the oil pan, until the oil pan was warm to touch
worked great.  On the next crank, it spun just like in summer, and the
start was fast.  Changing the oil to clean, lighter weight oil solved
the problem.  Temps were -15F to 0F everyday, and a 5W30 oil change
did wonders for the few weeks I needed it.]

In conclusion, to start an engine with poor compression, poor injectors,
or worn valves, coolant jacket heating makes allot of sense.  To start
an engine which has oil excessively viscous, heat the oil.

>
> Remember the carburetted cars of the 70's era? They has a snorkel on the air
> cleaner w/ a thermostatic valve to dirvert air intake. When cold, air was drawn
> from the baffle surrounding the exhaust manifold via an aluminum flex tube.
> Perhaps one of these can be adapted, or used as a model.
>
> --Nate