Preheating engines: Airplane engines versus auto engines

Why is it that here in the Northeast US seemingly no one preheats their
automobile engine before start-up in very cold temperatures? Is the long-term
damage the same for both autos and aircraft engines? If so, why do you
suppose auto owners don't typically do this? Is it because that most auto
owners do not keep their cars very long?

--
Peter

Lycoming says you can start without preheat down in the teens if you
use multiviscosity oil. As others have said, one of the biggest
differences from auto use is that aero engines are often flown less
frequently so there's less oil hanging around at startup. On the
other hand, that's true even in warm weather, though warm oil will be
redistributed more quickly.

I doubt that you did any harm. Convert all the degrees to Kelvin
temps and be comforted :-)

On 12/20/2007 9:24:28 AM, Paul kgyy wrote:

I doubt that you did any harm. Convert all the degrees to Kelvin
temps and be comforted :-)

Ha. Thanks, Paul.

--
Peter

On 2007-12-19 12:21:28 -0500, "Peter R." said:

Given any other day, I would have plugged the aircraft back in and scrapped
the flight

I know what I did has negative long term repercussions on my engine's health

I'm sure you must do some analysis in your head to judge the damage
inflicted on the engine in this case - otherwise, how could you judge
if scrapping a flight is the appropriate thing to do? I'm curious how
you quantify the 'long term repercussions'. Have you concluded, for
example, that not preheating in this case will:

- Reduce the TBO for your engine by 10 hours?
- Increase oil consumption by .2 qt/hour?
- Increase the risk of a catastrophic in-flight failure by 5%?

Clearly those are just some examples, but I would like to understand
what you have judged the impact of flying in this case would be.

A key to lubrication of any aircraft engine is how soon an oil fog can
be established in a crankcase. This takes a while - especially if the
oil is thick, as the bearing journal clearances are not that great and
the amount of oil thrown from them is minimal given starting oil
viscosity and the comparatively low crankcase activity at low rpm.
Most of the oil flow generated by that fixed volume oil pump ends up
blowing over the relief valve and dropping directly back to the sump,
giving the oil little access to the heat of the engine pistons and
cylinder heads. There are no features on the rotating machinery that
will centrifugally splatter oil blobs onto the cam surfaces. They
have to depend on previous operation for lubrication until the fog
gets more generally developed.

Oil viscosity can easily vary over a 100:1 range between moderately
cold start and normal operating values. The leakage from a journal
bearing will correspond inversely as that viscosity and directly as
the cube of the bearing clearance - which is also compromised by the
differential thermal expansion of aluminum vs steel.

Remember it isn't the bearings - it is all the expensive surfaces in
your engine that are starved in a cold start. And the operating
profile is almost always a full takeoff power after only a few minutes
of operation.

I do agree though that the OP didn't do any substantial damage to his
engine since it had been run so recently and since it has
Continental's bottom-of-the-crankcase camshaft.

Peter, this thread has grown way too long and ****y for me to go check if
you already have received this info, so please excuse any duplication. Mike
Noel hit on an important factor that did not seem to be followed up on about
a difference between aircraft and automobile piston engines. See the papers
at http://www.tanisaircraft.com/articlesresearch.html .

Stan


"Peter R." wrote in message
...
This time of year here in the Northeast US I always preheat my Bonanza's
IO520 engine with a Tanis heater and an insulated cowling/prop cover as it
sits in an unheated t-hangar. The result is that the oil temperature at
startup is around 105 degrees F, even if the outside air temperature is as
low as -15 degrees F.

Monday night I arrived at my t-hangar to discover that at some point
during
the day the line person accidentally pulled out the plug connecting the
Tanis
heater to the small extension cord I use to extend the plug to the outside
of
the cowling cover, so the aircraft had not been preheating. Outside and
inside temperatures were both a cold 25 degrees F.

Given any other day, I would have plugged the aircraft back in and
scrapped
the flight but in this case I had an Angel Flight patient waiting in
another
city for my arrival and I was already late. Thus I made the painful
decision
to start up the aircraft and allow it to low idle until the oil heated
thoroughly. A small consolation is that the engine had been recently
filled
with fresh Exxon Elite oil. To my relief the aircraft started right up.

I know what I did has negative long term repercussions on my engine's
health
and I have already derived a tool to lock the two cords and prevent this
accidental unplugging from happening again. However, this leads me to
question the differences between aircraft engines and auto engines:

Why is it that here in the Northeast US seemingly no one preheats their
automobile engine before start-up in very cold temperatures? Is the
long-term
damage the same for both autos and aircraft engines? If so, why do you
suppose auto owners don't typically do this? Is it because that most auto
owners do not keep their cars very long?

--
Peter

Stan Prevost wrote:
Peter, this thread has grown way too long and ****y for me to go check
if you already have received this info, so please excuse any
duplication. Mike Noel hit on an important factor that did not seem to
be followed up on about a difference between aircraft and automobile
piston engines. See the papers at
http://www.tanisaircraft.com/articlesresearch.html .

Even more interesting is that Tanis leaves such obsolete information on
their web site. Take a magnet to a few car dealerships and see how many
engine blocks are cast iron these days...


Matt

On Wed, 19 Dec 2007 12:21:28 -0500, Peter R. wrote:

Why is it that here in the Northeast US seemingly no one preheats their
automobile engine before start-up in very cold temperatures? Is the long-term
damage the same for both autos and aircraft engines? If so, why do you
suppose auto owners don't typically do this? Is it because that most auto
owners do not keep their cars very long?

No because it is entirely unnecessary.
--
Remove numbers for gmail and for God's sake it ain't "gee" either!

"Peter R." wrote in message
...
This time of year here in the Northeast US I always preheat my Bonanza's
IO520 engine with a Tanis heater and an insulated cowling/prop cover as it
sits in an unheated t-hangar. The result is that the oil temperature at
startup is around 105 degrees F, even if the outside air temperature is as
low as -15 degrees F.

Monday night I arrived at my t-hangar to discover that at some point
during
the day the line person accidentally pulled out the plug connecting the
Tanis
heater to the small extension cord I use to extend the plug to the outside
of
the cowling cover, so the aircraft had not been preheating. Outside and
inside temperatures were both a cold 25 degrees F.

Given any other day, I would have plugged the aircraft back in and
scrapped
the flight but in this case I had an Angel Flight patient waiting in
another
city for my arrival and I was already late. Thus I made the painful
decision
to start up the aircraft and allow it to low idle until the oil heated
thoroughly. A small consolation is that the engine had been recently
filled
with fresh Exxon Elite oil. To my relief the aircraft started right up.

I know what I did has negative long term repercussions on my engine's
health
and I have already derived a tool to lock the two cords and prevent this
accidental unplugging from happening again. However, this leads me to
question the differences between aircraft engines and auto engines:

Why is it that here in the Northeast US seemingly no one preheats their
automobile engine before start-up in very cold temperatures? Is the
long-term
damage the same for both autos and aircraft engines? If so, why do you
suppose auto owners don't typically do this? Is it because that most auto
owners do not keep their cars very long?

--
Peter

I've been more cautious about rapid heating up of engines since I
unfortunately split the engine block of my Jaguar XJ6 4.2 litre that I
conclude was caused by immediate rapid driving from -5c being late for an
appointment. Guess that expensive incident will always stay in my mind...

Mike

Mike Gilmour wrote:
"Peter R." wrote in message
...
This time of year here in the Northeast US I always preheat my Bonanza's
IO520 engine with a Tanis heater and an insulated cowling/prop cover as it
sits in an unheated t-hangar. The result is that the oil temperature at
startup is around 105 degrees F, even if the outside air temperature is as
low as -15 degrees F.

Monday night I arrived at my t-hangar to discover that at some point
during
the day the line person accidentally pulled out the plug connecting the
Tanis
heater to the small extension cord I use to extend the plug to the outside
of
the cowling cover, so the aircraft had not been preheating. Outside and
inside temperatures were both a cold 25 degrees F.

Given any other day, I would have plugged the aircraft back in and
scrapped
the flight but in this case I had an Angel Flight patient waiting in
another
city for my arrival and I was already late. Thus I made the painful
decision
to start up the aircraft and allow it to low idle until the oil heated
thoroughly. A small consolation is that the engine had been recently
filled
with fresh Exxon Elite oil. To my relief the aircraft started right up.

I know what I did has negative long term repercussions on my engine's
health
and I have already derived a tool to lock the two cords and prevent this
accidental unplugging from happening again. However, this leads me to
question the differences between aircraft engines and auto engines:

Why is it that here in the Northeast US seemingly no one preheats their
automobile engine before start-up in very cold temperatures? Is the
long-term
damage the same for both autos and aircraft engines? If so, why do you
suppose auto owners don't typically do this? Is it because that most auto
owners do not keep their cars very long?

--
Peter

I've been more cautious about rapid heating up of engines since I
unfortunately split the engine block of my Jaguar XJ6 4.2 litre that I
conclude was caused by immediate rapid driving from -5c being late for an
appointment. Guess that expensive incident will always stay in my mind...

No, that was caused by driving a Jaguar...

Matt

I've been more cautious about rapid heating up of engines since I
unfortunately split the engine block of my Jaguar XJ6 4.2 litre that I
conclude was caused by immediate rapid driving from -5c being late for an
appointment. Guess that expensive incident will always stay in my mind...


My guess would be that the very cold temps caused the block to split due
to the coolant freezing over night. If it was -5C when you started it,
chances are it was much colder at some point in the evening.

Common in the upper Midwestern US was to see 70's era cars blow out
freeze plugs and/or crack blocks by running no (or too weak) antifreeze.
A cold start and immediate run up to high speed should not cause
catastrophic failure of a block. Being a Jag, it may have had a badly
cast block since new. Their QC ain't the best.

Good Luck,
Mike