Water Pump Group
(1) Port (alternate heater supply). (2) Port (for engine diagnosis). (3) Ports (heater return).
The pressure rise (increase in pressure or pressure differential) tells if the water pump is operating correctly. Measure the pressure rise across or between port (1) or port (2) and one of two ports (3). Ports (1) and (2) represent water pump outlet pressure. Ports (3) represent water pump inlet pressure (suction). With the engine at operating temperature, under full load condition, the pressure rise must be a minimum of 80 kPa (12 psi).