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New type Thermostat for 1954
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  “A new engine cooling system thermostat (160º) will be sued in 1954 eight cylinder engines.  This thermostat does not have a gas filled bellows and, consequently, is not affected by pressure within the engine cooling system.  The thermostat has been referred to as a cartridge type containing a movable valve opened by pressure exerted by the expanding of a liquid contained in the cartridge which forces a plunger contained in a cylinder against the valve.  The valve is closed by spring pressure.  The cycle of operation then is the small plunger moving upward, opening the valve due to the expansion of the liquid beneath it; when the fluid contracts, the plunger moves down and the springs tend to close the valve.  This change was necessary because of the 13 lb. pressure system to be used on cars equipped with air conditioning.  No other thermostat should be used in 1954 eight cylinder engines.  The production thermostat (151º) will continue to be used in all six cylinder engines.”
  The above information came from Pontiac Service Craftsman News, No. 13 S-257  December, 1953.  This same issue announced the water pump seal was also changed due to possible use on an air conditioned car with 13 lb. system.  There was concern that the previously used seal would leak if subjected to the higher pressure.

  This information serves to illustrate the point that you should not install parts indiscriminately!