Re: Thermistats

[jlandry@domain.elided (John A. Landry)]

In a brilliant stroke of genius, Kevin Curry <kevin@domain.elided> blurted
out:

>"This is with the old style thermostat (like the Robertshaw) in place"
>
>Being new to this list, could you please explain what a "Robertshaw" thermostat
>is?

Apparently the Robertshaw Co. is now the only manufacturer left who makes a
thermostat for IH vehicles in the original style.  Stant used to make a
direct copy of the original IH design, but it was discontinued a couple of
years ago.  Who knows... Stant might have been the OEM thermostat supplier
to IH when Light Line was still in production.  Stant now offers
replacements that are like any other standard style thermostat you've ever
seen.

What's the difference between the two types?  The original style thermostat
has a cylindrical projection on the bottom that moves downward upon
opening.  Upon fully opening, it's thought that this projection acts to
partially or fully block the bypass port... verses the "standard" type
thermostat which doesn't do this.  Blocking the bypass port means all
engine coolant would be forced to pass through the radiator (and get cooled
off).  Having the bypass port left open means a portion of the coolant
always finds it's way back into the engine without getting cooled in the
radiator first.

IH must have originally chosen (or designed) a thermostat which blocks the
bypass port for a good reason!  It's theorized that by blocking the bypass
port on full thermostat opening, the cooling system capacity is increased
(because the constant leakage or bypassing of coolant through the bypass
hose is decreased or eliminated).  At low heat loads, the difference in
thermostat type is probably not very noticeable... the thermostat simply
compensating by opening further.  But at high heat loads (like when pulling
a trailer, etc.), the difference might be quite significant.  I haven't had
a chance to test this theory under summer conditions yet, but so far it
seems to bear out.

The original style thermostat would look something like this (view with
fixed pitch font)...

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           |              | <====== This is the important part!
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                Bottom

Take care,

John
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