Cummins/Onan — Flushing Cooling System
Maintenance
From a Cummins/Onan operator's manual — check it applies to your exact model before use.
Applies to: Cummins/Onan DGEA, Cummins/Onan DGFA, Cummins/Onan DGFB, Cummins/Onan 6CT8.3G engine, Cummins/Onan 6CTA8.3G engine
Before you start
- Excessive air pressure while starting water flow could split radiator core. Apply air pressure gradually to avoid damage.
Procedure
- Flush radiator and block after cleaning or before refilling with new coolant.
- Open upper and lower radiator hose connections and install radiator cap.
- Attach flushing gun nozzle to lower radiator hose connection and let water run until radiator is full.
- When full, gradually apply air pressure to avoid damaging core.
- Shut off air and allow radiator to refill. Repeat until water is clean.
- To flush engine block, remove thermostat to allow water to fill block.
- Attach flushing gun to upper radiator hose and fill block with water.
- Restrict lower radiator hose opening until block is filled.
- Apply air pressure and force water from lower opening. Repeat until water is clean.
- Replace thermostat and all hoses and refill cooling system.
Tools required
- flushing gun Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Full service-parts list: Cummins/Onan DGEA →, Cummins/Onan DGFA →, Cummins/Onan DGFB →
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.