Both a block heater and in place of glow plugs in the cylinder the ISB Cummins has a grid heater in the intake manifold , or incoming air path that warms the air when the outside temp is below a certian temp and untill the engine coolant reaches a certian temp and shuts off. The block heater warms the coolant and will run the grid heater for a shorter amount of time. I have my truck plugged in and on a timer and run it for about 2.5 hours in the morning which aids in quicker starting and faster coolant warm up.