车凉的时候就打开就不会

关键是“Begin with a cold engine. Remove the radiator cap and start the engine. Set your digital multimeter to DC volts at 20 volts or less. When the engine reaches operating temperature, insert the positive probe directly into the coolant”

目的是让coolant循环到radiator才能量准，这只有在coolant温度达到一定程度thermostat打开了才能循环。不过发动机转不转我测量的结果几乎没有差别。