The thermostat is used to maintain a minimum coolant temperature. This
is neccesary as the cooling capacity of the radiator is generaly way
higher that the heat production in an engine (in a proper working car).
As the radiator will cool down to much, the thermostat will restrict
flow so that the coolant in the engine can raise to the desired
operating temperature again.
It is not at all passive once the engine has warmed up, it controls the
engine's operating temperature. Without it the engine would run to cool.
Kees Oudesluijs
NL
> "The temperature is regulated by the thermostat, more or less."
> [TRUE, as long as coolant temperature is below the rated temperature of the
> thermostat]
>
> "If more heat is developed it will open further to allow
> more cooling..."
> [TRUE, as long as the thermostat is not already open to the max.]
>
> "...to drop the temperature to the set level."
> [NOT EXACTLY. The function of the automotive thermostat is not to maintain
> the coolant temperature at a "set" point (as in a house), but only to
> restrict the flow of coolant to the radiator until the engine warms up to
> operating temperature. The automotive thermostat is a completely passive
> device, responding to coolant temperature but not controlling it (except as
> it restricts coolant flow during warmup). At its rated temperature, the
> thermostat begins to open in response to increasing coolant temperature, and
> will continue to do so until it is wide open. At that point, it has no
> further ability to do anything to restrict coolant flow.
> It's a common misconception that installing a "lower temperature" thermostat
> will help to cool the engine.
>
> Steve Byers
> HBJ8L/36666
> BJ8 Registry
> Havelock, NC USA
> ----------------------
>
> Hmm,
> Not so sure about this. The temperature is regulated by the thermostat, more
> or less. If more heat is developped it will open further to allow more
> cooling to drop the temperature to the set level.
> The reading also depends on where the sensor is placed. In the cilinder
> head, intake manifold, thermostat housing, top of radiator etc.
> Changing over the thermostats may cast some light here? Just to see what
> happens.
> Kees Oudesluijs
> NL
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