IMO heating the operating element, or capsule, will ruin it. I've had
them fail from overheating in an engine that still had water in the
block (and wasn't otherwise harmed).
The Robertshaw 330 looks like a good candidate, in part because it has a
wide outer ring that can probably be spot welded, or even soldered to,
without overheating the capsule. Another possibility is the 337, which
has a separate spring loaded plate on the block end. (I believe it fits
VW Rabbit/Golf.)
Tony's choice of .400" for the skirt looks like a good compromise. It
will block the bypass port slightly when cold, but allow the limited
stroke (~.240" on a 330) to completely block the port when hot, at least
on a TR4 housing. (As I recall, the TR3 housing had a larger bypass
opening than the TR4.)
The TR4 housing I have isn't perfectly round, but 1.950 - 1.960" looks
like the right OD for the skirt.
When cold, the .400" skirt should rest against the sealing plate.
Randall
Tony Rhodes wrote:
> With the modern ones, the skirt will move inward from the flange toward the
> block. I have thought a bit about this before I found the XKs 'stat.
> It would be possible to make a brass hoop about .4" in width and of a diameter
> that will just comfortably clear the housing. The hoop can have two arms
> which can be arced over the thermostat and then can be spot welded
> to the "bulb" of the 'stat. The "bulb" is a nice place to make the attachment
> if it does not destroy the mechanism. I am not sure if it will cause
> damage or not...
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