Abstract: A downhole tool, comprising a housing; a sensor having components within the housing, the sensor being for monitoring a characteristic of a well; and one or more coolant supply lines extending to the components. A method comprising: monitoring a characteristic of a well using a sensor having components within a housing; and supplying coolant through one or more supply lines to the components. The methods and apparatuses may be used to drill steam assisted gravity drainage (SAGD) wells.