Abstract: The disclosure illustrates an air breathing liquid cooled compression ignition engine having a turbocharger and an aftercooler connected to the engine cooling system to lower the temperature of air compressed by the turbocharger. The engine cooling system includes a centrifugal pump having a pressure output that increases with increasing engine RPM. In order to minimize the generation of smoke during transient acceleration from idle, a flow control valve responsive to pressure differentials permits engine coolant flow through the aftercooler only when the engine is in its normal operating range above idle. The valve prevents the aftercooler from heating the intake air when the air delivered to the aftercooler during idle is lower than the temperature of the engine coolant.