Folks,
this all came from this months JEC magazine, which has a superb article on XK,
V12 and AJ6 engines, unleaded and overheating.
I have mailed the editor to ask if I could reproduce it on a web page.
Among all the information was the explanation of the difference between the
bellows thermostat and the later plunger type.
The bellows ones are needed one the cars which like the S-Type, the by pass is
simply a slot into the side of the thermostat housing… As the engine warms up
the bellows expands thge aperature is created by raising the top of the
thermostat and at the same time carrying a slide up around the circumference of
the bellows. This slide is the means by which the by-pass is shut off.
I fitted the to my S-Type the thermostat out of the later S-Type parts book,
C27650, which appears to cover all S-Types.
The earlier parts book has another number (similar C20766).
Problem is I can’t remember what the thermostat looked like.
The car heats up quickly and sits on 70C, and doesn’t overheat/
The article goes on to say
“Whilst it is not physically possible to fit an early-style thermostat to later
cars, unfortunately the later type will physically fit the earlier housings, but
the very nature of their operation means that they serve no purpose whatsoever
and therefor it will be as if no thermostat is fitted at all”
Also
“It is not unusual on an overheated engine that is not fitted with a thermostat
to have a situation wherby cold water poured on the cylinder head will boil off
the backs and yet the front will allow the water to pool. If the engine has
become this hot, the head will almost certainly be scrap.”
Also, the flow around the rear cylinders will be very slow, and localised
overheating could occur leading to dropped valve seats etc, while the
temperature gauge may show a low reading.
So, you can understand that while I have no indications that I have the wrong
one, I think I’ll take a look.
Perhaps there was a lated design that wasn’t a bellows type. That was why I was
asking about the C27650 part number, as I know that is what was fitted. Cost
all of 2.50 pounds.
Alastair Lauener
64 S-Type