I took out the airbox and aimed a hairdryer at the thermostat cartridge from about 4 inches away. The flapper moved but never completely closed the hot air intake. For now I removed the preheat hose from the exhaust manifold so the AMM wont be damaged.

Here in the Virginia mountains we sometimes get winter temperatures down to 0 deg F. What AMM inlet temperature is the airbox thermostat supposed to maintain ?

With the flapper forced to the "no hot air" position, what is the coldest outside temperature at which the engine will start and run well ?

It looks like the vacuum diaphragm in the airbox allows the ECU to admit some hot air even if the thermostat cartridge has closed off the hot air inlet. Under what conditions would the ECU do this ?

I could also replace the thermostat cartridge with a solid rod that keeps the hot air inlet closed unless the ECU activates the vacuum diaphragm.

Thanks,

Mike