What temperature do you plug in a diesel?

Diesel engines typically require block heaters to be plugged in when temperatures drop below 0°F (-18°C). In extremely cold conditions, such as below -20°F (-29°C), it may be beneficial to plug in even earlier to ensure easier starting and reduce engine wear. The specific temperature can vary based on the engine design and the type of diesel fuel used, so it's always best to consult the vehicle's manual for guidance.