Preheat

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