Engine warmup/operating temp. WAS: aero blades more fragile?

[Joshua Van Tol]

Tolerances are looser at cold temps, but that's actually a worse wear
condition, the oil film can't adequately cushion the piston and it bangs
around in the bore, causing excess wear. Also, the oil isn't flowing well
when cold.

The aluminum pistons have a greater coefficient of thermal expansion
(despite having some design features to control this) and they grow faster
than the iron block. Also the pistons run much hotter than the block.

Engine failure due to overheating can occur due to several reasons, but the
most common is the pistons growing enough to scuff the sides of the pistons
and the sides of the cylinder walls. Following that head gasket failure due
to the head growing too much lengthwise and bowing upward. Lubricant failure
can also occur, which can cause bearing failure. But the usual overheat
failure is the pistons scuff, compression is lost, and the engine quits.


On Fri, Dec 11, 2009 at 2:08 PM, <cobram at juno.com> wrote:

> Components do not contract when they're heated, they expand.  How can
> tolerances be tighter at  colder temps?  If this were the case, things
> would start seizing up after they got up to temp.
> An engine which is allowed to warm up at idle will last longer than one
> that is driven off the line cold, it's negligible but measurable.
> Increased friction because of cold lubricant, degradation of the
> lubricants by condensate and unburned fuel, less efficient heat transfer
> in a cold cylinder from the air-fuel mixture to the cold cylinder walls
> and pistons is what happens when an engine is warmed up, whether you let
> it idle or drive it immediately, it makes NO DIFFERENCE in engine and
> component wear characteristics.
> The real reason they want people to drive off the line with everything
> cold is to save gas and reduce emissions.  Both admirable goals, and with
> modern engine management and components there is no damage done doing so
> AS LONG as you drive very conservatively until everything warms up.
> Suggestions from manufactures et. al have nothing to do with components
> lasting longer or wearing less.
>
> BCNU,
> Yahoo nuked my website with no warning.
> "A government big enough to give you everything you want is a government
> big enough to take from you everything you have.
>
> Brett Dikeman <brett.dikeman at gmail.com> writes:
>
> > Nope, idling when the engine is cold.  Tolerances, mostly cylinder
> > wall-to-rings, which are designed to be 'right' at the proper
> > coolant
> > temperature, and are much tighter when the engine is cold.  The
> > only
> > thing it'll really effect long-term is compression, slightly.
> > Lower
> > temperature thermostats (or stuck-open thermostats) cause the same
> > problem.
>
> _______________________________________________
> quattro mailing list
> http://www.audifans.com/mailman/listinfo/quattro
> http://www.audifans.com/kb/List_information
>