Preheat

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

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"

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.

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)

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.

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

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

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

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.

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