Block heaters are worthless because they don't turn on until it's 0 degrees out,
the reason for this is if the OBD2 reads that the block is warm and it's should not be, there must be a bad sensor reading and it will set a code and give you a check engine light. I have a block heater in my Silverado and was surprised they wont operate above 0 degrees as the ones in older trucks I have owned would operate at any temp. but the new ones are thermostatically controlled.
