Preheat

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

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

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"

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"

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.

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

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

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.

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)

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"