Originally Posted by 85chedeng300D

anyway, my analysis tells me that the reason it is behaving weird like this is, i think that the fluid in the radiator is too cold when ambient temp is not that hot, therefore when the thermostat opens the cold water from the radiator immediately shuts the thermostat down until it becomes hot again to trigger it to open and allow the cold fluid to cool the engine again and shut the thermostat, and so on, hence the gauge fluctuation. hot. cold. hot. cold. hot. cold....