Cummins/Onan — Draining and Flushing the Cooling System
Maintenance
From a Cummins/Onan operator's manual — check it applies to your exact model before use.
Applies to: Cummins/Onan GGPA, Cummins/Onan GGPB, Cummins/Onan GGPC, General Motors GM 5.0 L engine
Before you start
- The heater element will burn out if engine coolant is removed with heater connected to power source.
Procedure
- Disconnect engine coolant heater from power source (if equipped).
- Allow the engine to cool and then remove radiator pressure cap.
- Open the radiator drain cock and remove the water drain plugs (one on each side of engine).
- When the coolant is drained, place the end of a water hose into the radiator filler and turn on water supply.
- Regulate the flow of water until it equals the outflow from drain openings; continue flushing until outflow is clear of rust sediment.
- If equipped with engine coolant heater, drain coolant by removing hose and clamp from bottom of heater.
- Replace the water drain plugs and close the radiator drain cock when flushing is complete.
- Refill the cooling system with the recommended coolant.
Source: Cummins/Onan operator's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.