Cold Starts

"Dennis O'Connor" wrote in message
...
Well, there's preheats and there's preheats...
A quick preheat with a red dragon makes you feel warm all over (so does
urinary incontinence while wearing a dark wool suit) but doesn't do much
of
anything except make the exterior sheet metal, fins, etc., temporarily
warm... The oil is still at ambient in the pan, and definitely ambient
upon
entering the oil pump... And that great steel slab of rotating oil
passages
they call a crank is still at -4 degrees, or whatever, to the oil trying
to
flow through it - chilling the 'supposedly' warm oil quite nicely and
instantly...
notice that the crank has two or more 'ambient temperature equalizing
heat
sinks' firmly attached......
Of course, you feel all warm and secure - if not actually doing a lot for
the engine - so I suppose that's worth something...

Same deal for an oil pan heater... You have a puddle of relatively warm
oil
(often with a chilled center if it is the typical preheat) that will
assume
crank/prop and case temperatures immediately upon flowing into the
passages...

If you read the aggregate wisdom of the alaskan/arctic flyers, you will
see
that a preheat includes a solid hour - and usually more - of a red dragon
with the pedal to the metal, cowl blankets and prop booties, pouring the
heated oil (from a stove) into the engine and immediately starting...

Now the Reif, et. al., systems of cylinder clamps and pan pads can be
helpful IF they are on for a number of hours with an good, metallized,
insulated, blanket tightly wrapped, booties on the prop and hub, and no
air
blowing up the exhaust, to allow the heat to soak all the way to the
center
of the crank... Less effort than that and you are kidding yourself...


denny

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.



"Dale" wrote in message "Dennis O'Connor"
wrote:

I started my engines this morning at -4 F... No preheat never do
That's the way this airplane has been treated ever since
semisynthetic, multiviscosity, oils came out.... Engines go to TBO
routinely...

Wow. To each his own. I would never start at those temps without
preheat, and I also used 15W50. I've also tried to pour it when it's
cold. G If it works for you, great.

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.

Aircraft engines are usually designed to turn at about 2700 rpm max. Auto
engines are designed to turn about 5000 to 6000 rpm max. Since the valves are
closing much more rapidly on an auto engine, the springs must be made much
stiffer. Since these stiffer springs slam the valve head against its seat with
much more force, the valves are made much thicker to take the punsihment.

In short, the entire valve train of an aircraft engine is much more delicately
built than that of an auto engine. Skip the preheat, and you run a serious risk
of snapping a valve.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way that
you look forward to the trip.

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

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

wrote in message
...
The oil is very thick

Is there any difference in viscocity between a 15/50 aero oil
and a 15/50 car oil?

Paul

Viscosity...

"Paul Sengupta" wrote in message
...
wrote in message
...
The oil is very thick

Is there any difference in viscocity between a 15/50 aero oil
and a 15/50 car oil?

Paul

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

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

Dennis O'Connor wrote:

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...

Pilot's handbooks are written by marketing departments, not engineers.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way that
you look forward to the trip.

As I understood it, the max engine damage is done just after starting,
before the oil is flowing properly, both in a car engine and a plane
engine. I know when it's cold it takes longer for my oil pressure to
come up, inferring that the oil is thicker when cold...also suggesting
that the oil isn't flowing to the important bits so quickly.

So I'd have thought that pre-heating (if done properly) would
extend the life of the engine by some amount rather than prevent
catastrophic failure.

Paul

"Dennis O'Connor" wrote in message
...
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?

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.

I use 15W50 in the Continental and 10W40 in the car. Not much difference.
Also, in the winter people run their Cont/Lycs on straight 30 weight. 30
weight is like water when at operating temps. I don't believe my O-200 runs
nearly as hot as a modern auto engine.

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.

Doesn't play. The pistons are aluminium and the bores are steel. In cold
weather the aluminium pistons shrink more than the steel cylinders and
clearance actually increases. The rings are steel and follow the cylinders.


-Cory

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

Dave Stadt wrote:
: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.

: Doesn't play. The pistons are aluminium and the bores are steel. In cold
: weather the aluminium pistons shrink more than the steel cylinders and
: clearance actually increases. The rings are steel and follow the cylinders.

True... except the piston is warmed by the first few seconds/minutes of
combustion much quicker than the steel cylinders. It's not the starting so much as
the dissimilar warmup. If the cylinders are pre-warmed, the temperature differential
to be transitioned through is lower. Granted it's engine preheater propaganda,
I believe there's some truth to the research in http://www.tanair.com/article6.html.

If you get high-time from your engine without preheat, then good for you.
Nobody said that cold-starts are the only cause of engine wear, and I'm sure that for
particular engines it's worse than others. As always, YMMV.

-Cory

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************