Preheat

[PaulaJay1]

Winter is comming to Ohio ( thou the 60 deg day today disagrees) and the
subject of engine preheat arrises. I have a Tannis for the cylinders and a pad
to heat the oil. I can call the FBO and have them plug it in an hour before I
arrive and the engine is, at least, not cold to the touch. Still there is the
time when I fly somewhere for dinner or overnight and park in the cold, cold
outside.

The question, why is preheat necessary?

If it is OK to start the engine cold when the temp is 60deg F and let the cyl
head temp go up to 500 or 600 deg, why is preheat recommended when the cold
temp is 10 or 20 deg? The percentage difference in the delta T is less than
10%. Are the engine parts that critical that this small percentage change
makes that difference?

I use 15/50 oil so the "cold" oil should be a good at the lower temp.

Chuck

[Roger Long]

Preheat is far more important on Lycoming engines because the camshaft is at
the top. Oil is supplied to the valve lifters only by being sprayed from
the camshaft and crankshaft bearings. Colder oil is thicker and does not
spray very well.

On oddity about the dynamics of the valvetrain is that the pressure of the
camshaft lobes on the lifter is highest at low RPM and least and high RPM.
The metal pressures on the lifters are very high anyway. Oil also cushions
and distributes the load of the cam lobes against the lifters.

Everything is therefore working against the lifters on startup. The oil has
drained off while the engine was not running, the oil is thick so doesn't
flow easily through the oil passages and bearings, the thick oil doesn't
spray well, the pressure of the cam against the dry lifters is highest due
to low RPM.

The high cam pressures bend the surface of the lifters microscopically and
the metal fatigues. Small pieces come out in exactly the same mechanism as
potholes forming in a road. Then the edges of the holes breakdown and the
"potholes" become larger. The lifters then start to wear away the camshaft.

The faster a good oil film gets established on the cam, the less chance
there is of lifter damage. Anything under 60 degrees carries some risk. We
preheat below 40. A single cold start when it is really cold can damage a
lifter.

--

Roger Long



"PaulaJay1" > wrote in message
...
> Winter is comming to Ohio ( thou the 60 deg day today disagrees) and the
> subject of engine preheat arrises. I have a Tannis for the cylinders and
> a pad
> to heat the oil. I can call the FBO and have them plug it in an hour
> before I
> arrive and the engine is, at least, not cold to the touch. Still there is
> the
> time when I fly somewhere for dinner or overnight and park in the cold,
> cold
> outside.
>
> The question, why is preheat necessary?
>
> If it is OK to start the engine cold when the temp is 60deg F and let the
> cyl
> head temp go up to 500 or 600 deg, why is preheat recommended when the
> cold
> temp is 10 or 20 deg? The percentage difference in the delta T is less
> than
> 10%. Are the engine parts that critical that this small percentage change
> makes that difference?
>
> I use 15/50 oil so the "cold" oil should be a good at the lower temp.
>
> Chuck

[Jay Honeck]

> The faster a good oil film gets established on the cam, the less chance
> there is of lifter damage. Anything under 60 degrees carries some risk.
> We preheat below 40. A single cold start when it is really cold can
> damage a lifter.

Which always leads me to this same question: Does anyone here have a
"pre-oiler" installed in their airplane?

It would seem so logical, yet I've never met anyone with one installed
(other than on big warbird engines...).
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Roger Long]

The preoilers oil everything except the cam and lifters. The Ney nozzles
spray oil directly on the cam and lifters but not until there is oil
pressure. Neither one is the answer to the Lycoming cam problem but the two
together probably are. You would still want to preheat though to be sure
the oil was thin enough to get onto the cams.

--

Roger Long



"Jay Honeck" > wrote in message
news:_Uykd.324061$wV.233990@attbi_s54...
>> The faster a good oil film gets established on the cam, the less chance
>> there is of lifter damage. Anything under 60 degrees carries some risk.
>> We preheat below 40. A single cold start when it is really cold can
>> damage a lifter.
>
> Which always leads me to this same question: Does anyone here have a
> "pre-oiler" installed in their airplane?
>
> It would seem so logical, yet I've never met anyone with one installed
> (other than on big warbird engines...).
> --
> Jay Honeck
> Iowa City, IA
> Pathfinder N56993
> www.AlexisParkInn.com
> "Your Aviation Destination"
>

[G.R. Patterson III]

PaulaJay1 wrote:
>
> The question, why is preheat necessary?

Most aviation engines turn fairly slowly. That allows the manufacturers to use valve
springs that are pretty weak, compared to those in an auto engine. That, in turn,
allows them to build the entire valve train pretty light. That's the weak point in
the design, and you can snap a valve stem if you don't preheat.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

[Rip]

Aluminum (like crankcases) shrinks faster than steel (like crank and cam
shafts). At some temperature (like 10 deg. F), there is NO clearance
left between the bearings and the crank. Starting the engine leads to
very rapid bearing and journal destruction.

PaulaJay1 wrote:
> Winter is comming to Ohio ( thou the 60 deg day today disagrees) and the
> subject of engine preheat arrises. I have a Tannis for the cylinders and a pad
> to heat the oil. I can call the FBO and have them plug it in an hour before I
> arrive and the engine is, at least, not cold to the touch. Still there is the
> time when I fly somewhere for dinner or overnight and park in the cold, cold
> outside.
>
> The question, why is preheat necessary?
>
> If it is OK to start the engine cold when the temp is 60deg F and let the cyl
> head temp go up to 500 or 600 deg, why is preheat recommended when the cold
> temp is 10 or 20 deg? The percentage difference in the delta T is less than
> 10%. Are the engine parts that critical that this small percentage change
> makes that difference?
>
> I use 15/50 oil so the "cold" oil should be a good at the lower temp.
>
> Chuck

[tony roberts]

> If it is OK to start the engine cold when the temp is 60deg F and let the cyl
> head temp go up to 500 or 600 deg,

CHT's of 500/600 degrees? Definitely not.

Tony

--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE

[Fastglasair]

>Does anyone here have a
>"pre-oiler" installed in their airplane?
>
>It would seem so logical, yet I've never met anyone with one installed

I have one on my Glasair Experimental. It is a Moroso (performance auto) unit.
It acomplishes 3 things. Pre-oil and pre-pressurize engine oil system 3 quart
capacity, Stabilized oil pressure (steady pressure), will maintain oil pressure
for the prop durring aerobatics.

[Ron Rosenfeld]

On 10 Nov 2004 23:37:55 GMT, (PaulaJay1) wrote:

>Winter is comming to Ohio ( thou the 60 deg day today disagrees) and the
>subject of engine preheat arrises. I have a Tannis for the cylinders and a pad
>to heat the oil. I can call the FBO and have them plug it in an hour before I
>arrive and the engine is, at least, not cold to the touch. Still there is the
>time when I fly somewhere for dinner or overnight and park in the cold, cold
>outside.
>
>The question, why is preheat necessary?
>
>If it is OK to start the engine cold when the temp is 60deg F and let the cyl
>head temp go up to 500 or 600 deg, why is preheat recommended when the cold
>temp is 10 or 20 deg? The percentage difference in the delta T is less than
>10%. Are the engine parts that critical that this small percentage change
>makes that difference?
>
>I use 15/50 oil so the "cold" oil should be a good at the lower temp.
>
>Chuck

Getting oil to flow easily is only one part of the problem. As you note,
this can be "solved" with a multi-viscosity oil.

But another important factor is the clearance between the pistons and
cylinders (or, more specifically, between the steel and aluminum parts of
the engine). Because of the differential expansion/contraction of the
different metals, at cold temperatures, clearance may be non-existent, so
there is markedly increased wear until the engine gets above some critical
temperature.

There's some good information on the Tanis web site.

By the way, I hope you didn't really mean to have CHT's 500-600°. Most are
redlined below that level.

Also, I would question whether one hour on the Tanis is long enough -- I
thought I had read someplace that three hours was advisable (with an
insulated cover) but I could be wrong.

I just leave my a/c plugged in all winter (in Maine). CHT's are usually
around 100°F and oil about 80°F and it starts up as readily as if it were
summer.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

[Jay Honeck]

> >Does anyone here have a
>>"pre-oiler" installed in their airplane?
>>
>>It would seem so logical, yet I've never met anyone with one installed
>
> I have one on my Glasair Experimental. It is a Moroso (performance auto)
> unit.
> It acomplishes 3 things. Pre-oil and pre-pressurize engine oil system 3
> quart
> capacity, Stabilized oil pressure (steady pressure), will maintain oil
> pressure
> for the prop durring aerobatics.

Thanks for the update. What engine is this installed on?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Fastglasair]

>Thanks for the update. What engine is this installed on?

IO-360-C1D6 Lycoming angle valve .

[[email protected]]

On 10-Nov-2004, tony roberts > wrote:

> CHT's of 500/600 degrees? Definitely not.


I presume he meant Fahrenheit, since he made reference to atmospheric temps
in F. 350 C = 572 F.

--
-Elliott Drucker

[[email protected]]

Ron Rosenfeld > wrote in message >...

A friend corroded the cylinders on his Cardinal from continuous
heating in just one winter. The water/acid boiled off the oil and
condensed in the cylinders on the bottom side. I understand Tanis
says that won't happen since they also have cylinder heat, but I'd be
more than a little scared of it still happening. If nothing else
minimize the preheat as much as convenient.

Lycomings especially need preheat to keep the cam from scoring. The
problem isn't bearings, it is all the expensive-to-repair surfaces
like cylinders and camshaft/lifter surfaces that depend on a fog of
oil for lubrication. Unfortunately if you push your luck on a cold
start, the fog isn't developed for some time as the oil that blows
over the relief valve has little access to the heat of the engine.
After it warms up and sprays from the bearings etc, it does.

[Jay Honeck]

>> CHT's of 500/600 degrees? Definitely not.
>
>
> I presume he meant Fahrenheit, since he made reference to atmospheric
> temps
> in F. 350 C = 572 F.

Cylinder head temps in that range are not recommended.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Matt Whiting]

wrote:

> Ron Rosenfeld > wrote in message >...
>
> A friend corroded the cylinders on his Cardinal from continuous
> heating in just one winter. The water/acid boiled off the oil and
> condensed in the cylinders on the bottom side. I understand Tanis
> says that won't happen since they also have cylinder heat, but I'd be
> more than a little scared of it still happening. If nothing else
> minimize the preheat as much as convenient.

Sounds like he had a defective heater. They shouldn't be gettings
things above 212F which would be needed to boil off water or acid.


Matt

[Ron Rosenfeld]

On 11 Nov 2004 14:15:44 -0800, ) wrote:

>A friend corroded the cylinders on his Cardinal from continuous
>heating in just one winter. The water/acid boiled off the oil and
>condensed in the cylinders on the bottom side.

He must have been doing something much different than I. I've been plugged
in all winter for the past fifteen years or so. The engine has been
overhauled twice during that time. No corrosion problems of the type you
describe.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

[tony roberts]

Still way too high.
Low EGT's maybe?

--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE


In article <9DQkd.342$fc.296@trnddc09>,
wrote:

> On 10-Nov-2004, tony roberts > wrote:
>
> > CHT's of 500/600 degrees? Definitely not.
>
>
> I presume he meant Fahrenheit, since he made reference to atmospheric temps
> in F. 350 C = 572 F.

[[email protected]]

On 11-Nov-2004, Matt Whiting > wrote:

> > A friend corroded the cylinders on his Cardinal from continuous
> > heating in just one winter. The water/acid boiled off the oil and
> > condensed in the cylinders on the bottom side. I understand Tanis
> > says that won't happen since they also have cylinder heat, but I'd be
> > more than a little scared of it still happening. If nothing else
> > minimize the preheat as much as convenient.
>
> Sounds like he had a defective heater. They shouldn't be gettings
> things above 212F which would be needed to boil off water or acid.


Strictly speaking, as you point out, the term "boiled off" was probably in
error. However, the point that moisture will be released as oil is heated
is not. If water is being held in suspension, heating the oil and the air
in the sump will cause some of that water to evaporate, and it may then
condense on cold surfaces. It's like when you blow on cold glass. The
moisture in your breath will condense and fog the glass, but your body temp
is surely well below 212 F. The acid he speaks of is probably dissolved in
the suspended water.

--
-Elliott Drucker

[[email protected]]

>
> Sounds like he had a defective heater. They shouldn't be gettings
> things above 212F which would be needed to boil off water or acid.
>
>
> Matt

Water vapor will slowly come off at much lower temperatures. All it
needs is to condense on something cooler than the oil. I don't recall
if he had crankcase heating only, or if he had cylinder heat too. I
recall the jug sitting above his desk at work, very thoroughly
corroded on the bottom in one winter.

[[email protected]]

>
> Getting oil to flow easily is only one part of the problem. As you note,
> this can be "solved" with a multi-viscosity oil.
>
> But another important factor is the clearance between the pistons and
> cylinders (or, more specifically, between the steel and aluminum parts of
> the engine). Because of the differential expansion/contraction of the
> different metals, at cold temperatures, clearance may be non-existent, so
> there is markedly increased wear until the engine gets above some critical
> temperature.

The differential expansion of aluminum vs steel is 6 microinches per
inch per degree F. Minimum bearing clearance is about .002 inch which
would take roughly 140 degrees of chilling to fully close up.
Probably even greater temps are needed for the cylinders to close up.
It is certainly a significant factor, but the reduced main and rod
bearing outflows (which goes as the cube of the clearance and
inversely as the viscosity) is also a reason there isn't much spray
inside a cold crankcase. All of these factors work against you,
especially on a new or fresh majored engine having minimum clearances.

Multi vis oils certainly help. Conversely having a summer weight oil
greatly increases the need for thorough preheating.

I use 32 degrees as a cutoff with 15W50, higher if it has been sitting
for more than a week. Below that I get an oil pump cavitation whine
on initial start on an O-320 E2D.

[Matt Whiting]

wrote:

>>Sounds like he had a defective heater. They shouldn't be gettings
>>things above 212F which would be needed to boil off water or acid.
>>
>>
>>Matt
>
>
> Water vapor will slowly come off at much lower temperatures. All it
> needs is to condense on something cooler than the oil. I don't recall
> if he had crankcase heating only, or if he had cylinder heat too. I
> recall the jug sitting above his desk at work, very thoroughly
> corroded on the bottom in one winter.

The original post said the water and acid boiled off, not evaporated.

A cylinder that is being used once in a while won't corrode as the oil
film from the last flight will protect it for at least a couple of
weeks. If he let his airplane sit the entire winter, then he had no
need to use an engine heater!


Matt

[Rip]

With minimum allowable bearing clearances, some engines have ZERO
clearance at about -10 degrees F. Cylinder choke and rapid heating of
the piston on cold start may also lead to piston scuffing. See
www.tcmlink.com for Continental's recommendations.

wrote:
>>Getting oil to flow easily is only one part of the problem. As you note,
>>this can be "solved" with a multi-viscosity oil.
>>
>>But another important factor is the clearance between the pistons and
>>cylinders (or, more specifically, between the steel and aluminum parts of
>>the engine). Because of the differential expansion/contraction of the
>>different metals, at cold temperatures, clearance may be non-existent, so
>>there is markedly increased wear until the engine gets above some critical
>>temperature.
>
>
> The differential expansion of aluminum vs steel is 6 microinches per
> inch per degree F. Minimum bearing clearance is about .002 inch which
> would take roughly 140 degrees of chilling to fully close up.
> Probably even greater temps are needed for the cylinders to close up.
> It is certainly a significant factor, but the reduced main and rod
> bearing outflows (which goes as the cube of the clearance and
> inversely as the viscosity) is also a reason there isn't much spray
> inside a cold crankcase. All of these factors work against you,
> especially on a new or fresh majored engine having minimum clearances.
>
> Multi vis oils certainly help. Conversely having a summer weight oil
> greatly increases the need for thorough preheating.
>
> I use 32 degrees as a cutoff with 15W50, higher if it has been sitting
> for more than a week. Below that I get an oil pump cavitation whine
> on initial start on an O-320 E2D.

[Roger]

On Fri, 12 Nov 2004 18:56:18 GMT, wrote:

>
>On 11-Nov-2004, Matt Whiting > wrote:
>
>> > A friend corroded the cylinders on his Cardinal from continuous
>> > heating in just one winter. The water/acid boiled off the oil and
>> > condensed in the cylinders on the bottom side. I understand Tanis
>> > says that won't happen since they also have cylinder heat, but I'd be
>> > more than a little scared of it still happening. If nothing else
>> > minimize the preheat as much as convenient.

When I start using the Tanis heater I leave it on all the time. I
have both the block and cylinder head heaters. The entire front end
of the Deb gets wrapped up in two layers of the new high efficiency
blankets. There is not a part on the engine where you can comfortably
lay your hand. I've been doing this now for about 12 years and over a
1000 hours of engine time.

>>
>> Sounds like he had a defective heater. They shouldn't be gettings
>> things above 212F which would be needed to boil off water or acid.

To boil it off, yes but it will slowly vaporize at lower temperatures.

>
>
>Strictly speaking, as you point out, the term "boiled off" was probably in
>error. However, the point that moisture will be released as oil is heated
>is not. If water is being held in suspension, heating the oil and the air
>in the sump will cause some of that water to evaporate, and it may then

If you heat only the sump there will be condensation.
If the whole front end is well insulated the cylinders should get
warm, but probably not warm enough to prevent condensation.

>condense on cold surfaces. It's like when you blow on cold glass. The
>moisture in your breath will condense and fog the glass, but your body temp
>is surely well below 212 F. The acid he speaks of is probably dissolved in
>the suspended water.

The acid is from the combustion products. I'd guess, mainly SO2 in
water. At 40C you won't find much condensation.

The first place to check is the top of the dip stick. If you have
visible water droplets there, don't leave the heater on except as
needed.

Nor would I leave it on if I didn't fly every week. At 40 to 50C the
oil's ability to "cling" is reduced greatly. Leave it more than two
weeks and I think you'll be starting on a dry cam.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com