An electric coolant heater assembly (10) has a coolant gallery (12) connected at each end to a fluid line of an engine's (E) coolant system (C). The gallery defines a fluid flow path through the assembly and includes baffles (24) for inducing turbulent flow to the fluid. A housing (20) mounted on one side of the gallery includes drive control electronics (18) for the assembly and a heater unit (14) is installed on the opposite side of the gallery. Heating elements (26) comprising the heater unit are energized by the drive control electronics. The drive control electronics are responsive to inputs from an external engine controller to operate an electric pump (P) and activate the heating elements so, at initial engine start-up, cause the coolant temperature to rise more rapidly than it otherwise would and assist the engine in reaching its nominal operating temperature faster than it otherwise would. Besides this initial engine warm-up assist, increased coolant temperature also adds to the amount of heat available to a heater (H) to heat the passenger compartment (PC) of the vehicle.