Cold Weather PreHeating

On Feb 2, 4:14 pm, "nrp" wrote:
On Feb 2, 3:52 pm, wrote:

We've started our airplanes at ambient temps as low as -25C (-13F)
without preheat, but they sure don't like it.

I'm surprised you got by with that. Must have been a Continental
engine?

Six Lycomings.

Lycomings have no crankshaft feature that will sling oil to
the camshaft lobes & most oil pump output has to flow over the relief
valve which has no access to the heat of the engine. It would be
interesting to find out how long it takes a genuine oil fog to
develop, My guess is quite a while.

Aeroshell 15W50 has the Lycoming-recommended additive to protect
the cam during dry starts. It has served us well.
The cam gets enough splash off the crank once the engine's running.
It's coming off the sides of the main and rod bearings.

Another factor is how long an engine has been sitting. A couple of
days is one thing, but if it has been two weeks a few more drops of
camshaft oil would have drained such that the need for preheat has to
be greater.

We hangar the airplanes every night at 5C. They start just fine at
those temps, six days a week. It's when they sit out at -25C for a few
hours that we have to get really careful, or for a weekend. They will
need preheat if they don't fire and stay running really early in the
attempt. With the frost and ice and snow around here they often need
hangaring anyhow.

We get the full 2000 hours out of them and could go another
500, easily. The compressions are in the mid-to-high 70s when they
come off, and there's no metal in the filters. The secret, I suppose,
is to run them frequently, and not for short 20-minute flights. And
use the Aeroshell with the additive. We had some cam problems before
switching to it. It costs more, but it costs less. Get the idea?

Dan

On Feb 2, 4:09 pm, Rip wrote:
According to Lycoming, an even bigger danger is that, at -10 deg. F,
engine tolerances are such that there may be zero, none, nada clearance
between important surfaces, like the crankshaft and it's bearings. The
aluminum case shrinks more than the steel crank, and one start under
those conditions will, not might but will, destroy the engine.

Rip

Here's Lycoming's take on it:
http://www.lycoming.textron.com/main...ldWeather.html

I don't see that they warn about destroying the engine.
Damaging it certainly is likely if care isn't taken. The aluminum case
shrinks at about twice the rate of the steel crank, but the crank's
bearings are steel half-circle shells that are in crush (ends butted
against each other) in the case bores. They will shrink at the same
rate as the crank and prevent the case from binding the crank too
much. Bigger danger in cold weather is running the engine too hard
before the steel cylinder barrels have warmed up; the aluminum piston
can expand enough to cause scuffing as the clearances disappear.
Engine shops see that frequently enough. The two-stroke engines in
ultralights are particulary fussy that way.

IIRC: Coefficient of linear expansion of aluminum is .1244
units per degree F; of steel it's .0655. I'd have to look it up to get
it exact.

Here's Lycoming's take on it:
http://www.lycoming.textron.com/main...ldWeather.html

I don't see that they warn about destroying the engine.

It is interesting that Lyc only says to expect "minor" wear
abnormalities with improper cold weather starting. That is pretty
watered down compared to some of the gloom and doom stated here and
elsewhere.

Until somebody is prepared to take a shiny new engine, cold start it,
and immediately tear it down for inspection, we may never know.

Good Luck,
Mike

"Aeroshell 15W50 has the Lycoming-recommended additive to protect
the cam during dry starts. It has served us well.
The cam gets enough splash off the crank once the engine's running.
It's coming off the sides of the main and rod bearings."

Dan -

From what I have seen inside Lycoming engines (and that's not very
many although they are all very similar) a small amount of leaking oil
from crank or rod journals isn't going to impact the cam surfaces very
soon after a really gooey & sticky oil startup. I suspect the cam is
going to have to rely on the residual oil from the last shutdown, for
some time - maybe even minutes for a difficult cold start - until an
oil fog environment is established. Laying a crankshaft next to a
camshaft & looking at the axial alignment of the two, The likely
initial oil splatter patterns look to me like they would miss the cam
surfaces.

A really interesting test would be to cut a hole in the side of a
junkable crankcase and examine the startup spray pattern.

Obviously you are doing something right. We both use the Shell
15W50. I've run counter to one of your "secrets" though in that I've
had a lot of short flights over 31 years to get to 1700 hrs TTSN on a
still solid Lycoming O-320E2D, only being religious about oil
preheats.

Maybe the presence of residual oil is more critical - in which case
the need for preheat would greatly increase for an aircraft sitting
for a few days. Might that jibe with your experience?

Mike Spera wrote:
Until somebody is prepared to take a shiny new engine, cold start it,
and immediately tear it down for inspection, we may never know.

Exactly. Just about everything you read on this subject is folklore and
speculation. There is little data or scientific method.

On Feb 5, 8:43 am, Dave Butler wrote:
Mike Spera wrote:
Until somebody is prepared to take a shiny new engine, cold start it,
and immediately tear it down for inspection, we may never know.

Exactly. Just about everything you read on this subject is folklore and
speculation. There is little data or scientific method.

It might be speculation but it's working for us. When
there is a lack of hard experiential data, you go by your own
experience, being careful not to make large changes. Many folks are
scared to operate engines in climates vastly different from what
they're accustomed to, and that's probably wise. It's not safe to
assume that the thing will behave as usual.

Dan

wrote:
On Feb 5, 8:43 am, Dave Butler wrote:
Mike Spera wrote:
Until somebody is prepared to take a shiny new engine, cold start it,
and immediately tear it down for inspection, we may never know.
Exactly. Just about everything you read on this subject is folklore and
speculation. There is little data or scientific method.

It might be speculation but it's working for us. When
there is a lack of hard experiential data, you go by your own
experience, being careful not to make large changes. Many folks are
scared to operate engines in climates vastly different from what
they're accustomed to, and that's probably wise. It's not safe to
assume that the thing will behave as usual.

Don't mean to discount your experience. Experience is good. Yours is
most probably more extensive than mine.

On Feb 4, 1:19 pm, "nrp" wrote:
"Aeroshell 15W50 has the Lycoming-recommended additive to protect
the cam during dry starts. It has served us well.
The cam gets enough splash off the crank once the engine's running.
It's coming off the sides of the main and rod bearings."

Dan -

From what I have seen inside Lycoming engines (and that's not very

many although they are all very similar) a small amount of leaking oil
from crank or rod journals isn't going to impact the cam surfaces very
soon after a really gooey & sticky oil startup. I suspect the cam is
going to have to rely on the residual oil from the last shutdown, for
some time - maybe even minutes for a difficult cold start - until an
oil fog environment is established. Laying a crankshaft next to a
camshaft & looking at the axial alignment of the two, The likely
initial oil splatter patterns look to me like they would miss the cam
surfaces.

A really interesting test would be to cut a hole in the side of a
junkable crankcase and examine the startup spray pattern.

Obviously you are doing something right. We both use the Shell
15W50. I've run counter to one of your "secrets" though in that I've
had a lot of short flights over 31 years to get to 1700 hrs TTSN on a
still solid Lycoming O-320E2D, only being religious about oil
preheats.

Maybe the presence of residual oil is more critical - in which case
the need for preheat would greatly increase for an aircraft sitting
for a few days. Might that jibe with your experience?

That would be wise. I wish someone would certify a simple
preoiler for these engines. There's a system operated by an electric
oil pump, but it seems to me that an accumulator that stored oil from
the system while the engine was running, and released it via a
solenoid controlled by the pilot immedialtely before start, would be
better and lighter. It could include a small electric heating element
that would warm the oil in it, and would inject oil into the galleries
as well as into a couple of spray nozzles that would fog the inside of
the case with the warmed, thin oil.
Even better would be a drilled camshaft that would have small
oil ports in the lobes, or even right next to the lobes, to get the
lifter faces wet.

Dan

writes:


That would be wise. I wish someone would certify a simple
preoiler for these engines.

I rather liked the idea of something that you stuck down
the dipstick hole and oh, blew compressed air in, I guess;
in any case spraying oil here there & everywhere...

[Not to say it would work, but it sounds intriguing...]

Hmm; how about a spiral shaft that you spin on a drill?
The end dips into the pan....
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

On Feb 5, 11:46 am, David Lesher wrote:
writes:
That would be wise. I wish someone would certify a simple
preoiler for these engines.

I rather liked the idea of something that you stuck down
the dipstick hole and oh, blew compressed air in, I guess;
in any case spraying oil here there & everywhere...

[Not to say it would work, but it sounds intriguing...]

Hmm; how about a spiral shaft that you spin on a drill?
The end dips into the pan....
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

The Lycoming has some of narrow slots in the bottom of the case under
the camshaft, and below that is the oil pan. The idea is to keep
engine vibration from throwing too much oil up into the rotating
machinery, while allowing the oil flung off the crank to drain. The
oil fog might have some difficulty reaching the camshaft, and cold oil
won't fog much, anyway.
Too much oil mist or spray overwhelms the oil control rings on the
piston. They can't scrape it all off at the piston speeds encountered
at higher RPM, and begin to float on it. The oil gets into the
combustion chamber and is burned, making smoke, using a lot of oil,
and carboning things up too much. It's just one reason worn-out
engines will use more oil; the bearings get looser and allow more oil
past them, which is then thrown into the cylinder. The oil pump is
made about four times larger than necessary to allow for this
increased flow as the engine wears. Early on, the excess is dumped
through the relief valve back into the case, but as things get old the
relief valve passes less and less until it's shut altogether, and now
you'll see the oil pressure start to drop.

Dan