[Healeys] Bellows Thermostats

[Bob Spidell]

You speak the truth.

re: "... There are replacement wax thermostats available with the bypass 
port block-off ring but they are not particularly cheap."

Typically a Robertshaw stat with the ring soldered on.  I have one 
installed; can't say it's worth more than a degree or two at most; but 
Robertshaw appears to be a solid brand.

One question, though: I think Moss and maybe other vendors sell a repop 
bellows type; anyone know if they're fail-close?

Bob


On 9/3/2017 8:41 PM, A H List wrote:
> Avoid the bellows thermostat, they are all old now and as you noted,
> fail closed. I put one in my engine and it failed within three months,
> fortunately without engine damage as I saw the temp rising.
>
> If you look at the design, they don't really block the bypass flow,
> more they limit it somewhat. The bypass port is radial and it doesn't
> actually seal in any way, the ring just comes down in front to reduce
> the flow. Modern engines have the same principle but have a
> spring-loaded disc instead of a ring and the disc seals over the
> bypass port axially.
>
> The vast majority of engines run just fine with the later wax stat as
> long as the system is in good shape and the car doesn't spend a long
> time idling in traffic. There are replacement wax thermostats
> available with the bypass port block-off ring but they are not
> particularly cheap. Considerably cheaper than an engine reco due to
> overheating though.
>
> Andy.
>
> On 9/4/17, Harold Manifold <manifold at telus.net> wrote:
>> Hello,
>>
>> I am in the process of putting my AH 3000 engine back together and went
>> looking for a recommendation for the engine thermostat. I was expecting to
>> find a recommendation for the opening temperature but instead found
>> information that recommends a bellows type thermostat should be used and
>> the
>> bellows is important or some of the coolant can bypass the radiator when
>> the
>> thermostat opens. If a bellows type thermostat is recommended is the
>> correct
>> type either the Smiths 85025 series or the AC Delco TF series? Is there a
>> modern replacement bellows type thermostat that fails in the open position?
>>
>> Your comments and insight is welcomed.
>>
>> Harold
>>
>> 1960 BT7
>>
>>
>>
>>