A few responses:
It’s correct to talk about the working material “boiling” if it’s a bellows thermostat, which works with an liquid alcohol charge. In the case of wax thermostats, “melting” is close, but a more correct term would be “liquifying”. As a point of interest, thermowaxes are amorphous solids, and don’t have a specific melting point. They transition from liquid to solid in a critical temperature range. (Think about leaving butter out on the counter. It doesn’t exactly melt, it goes soft and gets still softer as it warms. Get it warm enough and it’s a liquid.) That’s why we can talk about “start of open” vs “full open” for wax thermostats. You really can’t do that for bellows thermostats, because the transition occurs at a specific temperature.
It wouldn’t be completely incorrect to say that the materials expand due to exposure to heat. But a steam engine doesn’t work on warm water. The entire point is that the phase change…from liquid to vapor or from solid to liquid…is accompanied by great expansion. The expansion graph in Chapter 1 is really what happens to a thermowax as it warms. Because that curve is an immutable physical property of the wax, the thermostat will open at precisely the same temperature, every single time.
Peter Crespin’s comment is a common misunderstanding…the only E-Types that had bellows thermostats were the early 3.8’s. Jaguar transitioned to wax thermostats late in 3.8 production. In fact, the E-Type 4.2 S1 manifold was deliberately configured NOT to accept a bellows thermostat.“Bellows” refers to the motor used to open the thermostat, not to the configuration of the bypass sleeve. This will become clear by the time I’m done with the Bypass chapter. I can see that there are many surprises coming.
David. Thanks for referring to the E-type UK forum. That thread was one of the things that kicked this project off. That particular thread had a lot of valuable information, but also a lot of misconceptions. One of the reasons that I chose to publish this as a web book is that I don’t want to muddy the text with red herring discussions. So the discussion will be confined to Jag-Lovers, and I’ll incorporate only the information that’s accurate and consistent. That way it will become an enduring reference.
Marek. I placed a link to the IGI website in my Sources page. IGI is a major producer of thermostat wax. There may be enough info on their website to satisfy your curiosity. I’ll go into this a bit deeper in the September update.