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Several months ago there was a discussion about the suitability of old style bellows thermostats in pressurized cooling systems that generally came into use in 1941. It was stated that pressurized systems would alter the performance of the bellows style and should not be used in a pressurized system.

I stayed out of the discussion not having time to research the answer that would show this to be a myth/misunderstanding.

Below is an ebay listing for a Bridgeport/Robertshaw bellows thermostat with an application listing from their catalog, note that the bellows type is listed for many cars with pressurized systems.

Here I have a New Old Stock N.O.R.S Low temperature thermostat opens at 155 for 1948-1956 Austin, 1953 Buick Special, 1932-1952 Buick all, 1936-1956 Chevy all , 1946-1955 Frazer Kaiser, 1945-1955 Henry J, 1955-1956 Hudson V8, 1939-1956 Olds, 1935-1956 Packard 6, 120, 8, Clipper, 1955-1956 Pontiac, 1939-1954 Studebaker Champion, 1939-1956 Willys all and Jeep,

This is probably one of the subjects that will never be resolved to everyone's satisfaction. For what it's worth Packard switched to the capsule type thermostat during 1953 production and their reasoning was because increased pressure up to a certain point would tend to keep the bellows thermostat closed longer before it would fully open resulting in a potential overheating issue. Here is their explanation.

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Thanks, learned something new today. Thermostat manufacturers were unaware of that and certainly sold zillions of bellows t-stats for pressurized systems.

Next time I have a chance I'll put a bellows t-stat in my 52 and compare temperatures.