D 350 Pickup L6-359 5.9L DSL (1989)
Water Pump: Testing and Inspection
The water pump pulls coolant from the bottom of the radiator and pumps it through the engine back to the top of the radiator for cooling. Reduced or
interrupted flow will result in the engine running hot.
The pump is belt driven from the crankshaft pulley. An automatic belt tensioner is used to prevent the belt from slipping on the pump pulley. A
malfunction of the tensioner will cause the water pump impeller to rotate at a slower speed reducing the amount of coolant flow.
The coolant flow can also be reduced if the inlet hose to the water pump collapses. A hose will usually not collapse while the engine is running at low
speed. Check the hose while the engine is running at rated speed.
NOTE: Be sure the engine is warm, a minimum of 83°C [181°F], so the thermostat is open.
