Cold Starts

The threat of the aluminum case shrinking to the point of seizing onto the
steel crank due to the differential in expansion rate of the two materials
is more theoretical than real... Ignored is the fact that the bearing shells
are steel cylinders and will compress only so much when the case shrinks,
else they would buckle and collapse...

The argument of "it is the liquid cooling that makes the difference",
ignores the engineering fact that modern liquid cooled engines have vastly
tighter clearances than air cooled engines, not the other way around... So,
low temperature starts should be a hundred times more damaging to the engine
on your car by that theory... Yet my aluminum block/steel crank automobile
engine, which has such tight clearances that the owners manual calls for a
5W20 as the standard oil, - I actually use 10W30 - started the other
morning at -14F yup, 14 below and is still running fine, no knocking, no
oil smoke, no crushed bearing shells, etc...

As I spoke about in my diatribe on preheating, yesterday; most of what is
passed from cfi to student is an old wives tale endlessly repeated... And
yes, some of those OWT's find their way into the pilots handbook from
engineers who ought to know better...

As far as the comment about cylinder choke - yup, it exists - but come on
guys, think!... The cylinder sleeve is steel, the piston is aluminum... So
the piston will shrink more than the cylinder at very low temperatures, not
the other way around... There is no interference fit and no binding on start
up...

Let me post a challenge... Who knows of an engine that was actually damaged
and had to be overhauled because of cold starts without a preheat? Nope,
not the story of a guy I know told me about so and so... What engine do you
have first hand knowledge of, that was burned up on your airfield because of
a cold start? Doesn't exist!

I can start my engine every morning all winter long with no preheat, and you
start your engine once every two weeks with preheat, and I will have less
wear on my engine than you will...
denny

wrote in message
...
Dave Stadt wrote:
: How come the engine in my car with 190,000 miles is running fine with no
: signs of undue wear with nary a single preheat. It is often started at
: temps well below 0 F. Aluminium block, steel crank, steel cylinder
liners
: and aluminium pistons same as the ole Continental.

Two words: Liquid cooling. Everything about the aircraft engine is
catered to
running at ridiculously high temperatures during normal operation. The
oil is very thick
so it still lubricates at high temperatures and carries heat away from the
cylinders. The
cylinders themselves have choke (they're slightly smaller bore at the
top), with the
thought being they'll expand to be straight when they heat up during
normal operation.
Those two things are the primary reasons.... lack of oil and scuffing of
cylinders.

-Cory

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