Tesla certainly demonstrated the importance of direction of flow.
http://en.wikipedia.org/wiki/Tesla_valve

Allen
Ps: Thanks for changing the tag.

> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
Of
> Bob Blick
> Sent: Saturday, November 22, 2014 4:26 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [OT] Cars in general, was Best DIY Puffer HoneyTrap
>=20
> Changed the tag. Thanks Ariel for reminding me :)
>=20
> Yes and no. It all depends on the car.
>=20
>  In a Miata, if you remove the thermostat, cylinder #4 runs much hotter
>  than the others. If you are also flogging the car on a hot day, it's
>  more likely to overheat because #4 boils and then you lose coolant and
>  you're in trouble.
>=20
> The engine was originally designed for sideways mounting. When it was
> re-engineered for the Miata, they reversed the direction of the water
> flow, and a portion of the cooling for #4 became the heater core. The
> water flow was calculated based on the restriction of an open
> thermostat. With no thermostat, the flow is reduced through the heater
> core and #4.
>=20
> Lots of times when people turbocharge Miatas, they will re-plumb the
> cooling system to restore the originally-designed direction, and they
> get more even cooling that way.
>=20
> Bob
>=20
>=20
> On Sat, Nov 22, 2014, at 01:09 PM, Allen Mulvey wrote:
> > A motor vehicle engine does NOT run hot if you remove the thermostat.
> >
> > > -----Original Message-----
> > ...
> > >      Or if you leave the thermostat out the engine will run hot
because
> > > the coolant is going too fast to pick up the heat. This violates one
of
> > > the laws of thermodynamics and I don't remember which one. The reason
it
> > > runs hot is because most cooling systems have a bypass hole so that
> > > coolant will circulate through the engine when the thermostat is
closed.
> > > If the thermostat isn't there hot coolant is being directed right bac=
k
> > > into the engine without going through the radiator. On some engines
the
> > > hole was only about a quarter of an inch in diameter. In some engines
> > > the hole could be close to two inches. That is a lot of coolant that
> > > never makes it to the radiator.
> >
> > The bypass hole serves two purposes. It helps relieve the back pressure
> > on
> > the water pump when the thermostat is closed and it allows the HOT wate=
r
> > to
> > continue to circulate through the engine so it heats up faster. When yo=
u
> > remove the thermostat most of the hot water goes into the radiator and
> > cold
> > water from the radiator enters the engine, keeping it cool. The only
> > problem
> > you have if you remove the thermostat is that sometimes, in cool
weather,
> > the engine never warms up. Try it. I have.
> >
> > Allen
>=20
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>=20
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