Tim, thanks for testing the thermostat. You appear to be the only one with a 'true' bypass thermostat.
Sure wish a true bypass thermostat was still available. It would be nice to replicate the original cooling system designed for the 261 by the GM engineers.
The best solution seems to be to use a 235 housing with a couple holes drilled through the thermostat...or use the NAPA thermostat in the 261 housing with the bypass hole plugged. Either solution would function the same way. Both would allow some coolant to flow through the radiator to the engine with the thermostat closed. The 261 version preserves the original housing but sacrifices the screw that secures the fuel and vacuum lines that are part of the 235 housing.
NOTE: THE 261 HOUSING WITH THE NAPA THERMOSTAT STATEMENT IN THE ABOVE PARAGRAPH IS INCORRECT. COOLANT WOULD NOT GET THROUGH THE CLOSED THERMOSTAT TO THE RADIATOR AS IT WOULD WITH A DRILLED 235 THERMOSTAT.
