In article ,
Winston wrote:

Bruce L. Bergman wrote:
On Tue, 29 Dec 2009 11:01:38 -0800, Winston
wrote:

Bruce L. Bergman wrote:

(...)

Odds are long, but it could happen - Toilets usually don't get
thermally stressed at all,
They are under daily thermal stress, yes?

Yes, but when the furnace kicks on the heat is diffuse enough to
gradually raise the temperature of the water closet over the course of
an hour, at a slow rate and evenly all over.

I was delicately referring to the process of defecation.
It's 98.6 F over a couple square inches for more than 10 seconds.
You consider that a large temperature gradient. I don't.

The porcelain does not shatter.

You are heating the inside only, and at a very high rate. It's not a
given, but I can see an occasional toilet failure you could trace back
to this practice...

Nonsense. Toilets fail due to worn plumbing parts in the tank.
They don't crack even when we take a dump in mid winter temperatures.

Consider the porcelain spark plug. It sees a 200 F to 3500 F to 200 F
transition every other revolution. My cars go 100,000 miles between
plug changes. The old plugs come out looking moderately worn but
still quite serviceable. The plugs don't crack in normal use.

(...)

Dumping in a kettle-full of almost-boiling water from the stove is
going to throw in a whole lot more BTUs (guessing 10X to 50X) and over
a period of a few seconds than almost a minute.

The whole process was over within about 10 seconds with a
maximum temperature of about 100 F. I showed the arithmetic
in a previous post. There really is nothing to worry about.

The temperature coefficient of porcelain is quite low, 2 to 4 parts per
million per degree centigrade, which is what allows massive objects
(like sanitary fixtures) to be made cheaply, without having to gradually
cool for weeks after firing at 1500 degrees centigrade.

A useful discussion appears in US Patent 5614448.

I suppose someone could perform the obvious test on a junked bowl and a
large pot of boiling water.

Joe Gwinn