The heated and expanded wax causes the thermostat to open against spring
pressure. As the wax cools, the valve is closed by the spring pressure, not
"suction" of contracting wax, which would probably cavitate anyway.
As such, when the wax is lost there is nothing to push the valve open and
the spring returns it to the closed position, so failing in that position.
I agree that the older mechanical versions fail closed.
The Mocal version of oil thermostat bypasses the cooler when "closed".
Duncan McF
----- Original Message -----
From: "Nigel Graham" <nigel_graham@btclick.com>
Sent: Tuesday, January 24, 2006 9:11 AM
Subject: Re: Europa-List: Oil Thermostat
> <nigel_graham@btclick.com>
>
> Wax thermostats used in cars were notorious for failing closed
> (overheating
> the engine) since the wax capsule would split and the wax escape. It was
> the
> bi-metallic thermostats that failed safe.
>
> I have no idea how this oil 'stat fails but would guess closed.
>
> Nigel
> ----- Original Message -----
> From: "Duncan McFadyean" <ami@mcfadyean.freeserve.co.uk>
> To: <europa-list@matronics.com>
> Sent: Monday, January 23, 2006 11:15 PM
> Subject: Re: Europa-List: Oil Thermostat
>
>
> <ami@mcfadyean.freeserve.co.uk>
>
> More often in the open position, AFAIK.
> Cars with failed thermostats tend to run cold, rather than the reverse.
>
> Duncan McF.
> ----- Original Message -----
> From: "Mike Parkin" <mikenjulie.parkin@btopenworld.com>
> To: <europa-list@matronics.com>
> Sent: Monday, January 23, 2006 9:53 PM
> Subject: Re: Europa-List: Oil Thermostat
>
>
>> <mikenjulie.parkin@btopenworld.com>
>>
>> Duncan,
>>
>> If the waxstat fails does it fail open, closed or in the position where
>> it
>> failed.
>>
>> regards,
>>
>> MP
>>
>>
>>
>> ----- Original Message -----
>> From: "Duncan McFadyean" <ami@mcfadyean.freeserve.co.uk>
>> To: <europa-list@matronics.com>
>> Sent: Monday, January 23, 2006 9:43 PM
>> Subject: Re: Europa-List: Oil Thermostat
>>
>>
>>> <ami@mcfadyean.freeserve.co.uk>
>>>
>>> Yes they do (i.e. open very rapidly within a few degrees) around the
>>> temperature that they are 'rated' for, and close less rapidly. If you
>>> try
>>> it
>>> in water you'll see what I mean; an element rated at 80 will be doing
>>> next
>>> to nothing at around 78, then be fully open by about 82.
>>> Having to dig deep in memory for this one!
>>> If the temperature at any time exceeds 140 C then the wax element is
>>> permanently destroyed.
>>>
>>> Duncan McF.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>
>
>
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