> I'd guess any
> good physicist interested in thermal dynamics would lay this story low.
Well, I doubt this was developed solely on the TR motor. _All_ cars (at
least those with water cooled engines and thermostatic water flow
controls) have a bypass in one form or another, it's simply a
necessity. You may not be able to find it in all the other tubes, hoses
and wires on your Honda (or whatever), but it's there !
It makes plenty of sense from a physics standpoint too, water simply
does not conduct heat very well. I get proof of this every morning when
I turn on the 'hot' water in my bathroom and it takes several seconds to
get hot water, even though the other end of the pipe is heated to a
Thus, in a car engine running with the coolant flow completely blocked
off, the water _will_ reach boiling around the exhaust valve seats
before the water next to the thermostat gets hot enough for the Tstat to
open. This may be only 'nucleate' boiling, that is the steam bubbles
may collapse as soon as they spread into the cooler water, but it does
create excess thermal stress in the head. BTW, TR cylinder heads are
cast iron, which is notoriously brittle and prone to cracking from
I'm not saying that blocking the bypass will guarantee cracking the
head, lots of people "get away" with it. But, I definitely agree with
TeriAnn that blocking it completely is a _bad_ idea.
If there are any original TR4 owners still reading this rant, any
comments on whether the factory used the sleeved thermostat in TR4s ?
The illustration in my TR4A parts catalog shows a non-sleeved thermostat
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