Cummins/Onan — Cooling System Draining and Flushing
Maintenance
From a Cummins/Onan owner's manual covering: 4A2.3, 4A2.3-GS/GC, 6A3.4-GS/GC-1, 6A3.4-GS/GC-2, 6AT3.4-GS/GC, ES-1788. Check it applies to your exact model before use.
Applies to: Cummins/Onan ES-1788, Cummins/Onan 4A2.3 engine
Before you start
- Hot coolant is under pressure; do not loosen cap while engine is hot.
Procedure
- Disconnect coolant heater from AC power, if equipped.
- Allow system to cool; remove radiator pressure cap.
- Open radiator drain cock and disconnect lower radiator hose.
- Remove cylinder block drain plug or disconnect tank heater.
- Allow system to drain completely.
- Reinstall cylinder block drain plug or reconnect tank heater.
- Close radiator drain cock and reconnect lower radiator hose.
- Fill cooling system with clean water; do not install radiator cap.
- Operate engine for 5 minutes with coolant temperature above 194°F (90°C).
- Shut off engine and drain cooling system; repeat flush if water is dirty.
- When flushing water is clean, drain completely and refill with coolant.
Specs & values
- Flush temperature: above 194°F (90°C)
Full service-parts list: Cummins/Onan ES-1788 →
Source: Cummins/Onan owner'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.