Cummins/Onan — Cooling System Flushing
Maintenance
From a Cummins/Onan owner's manual covering: 230NT2, 230NT4, 250NT3, 275NT6, 275NTA1, 300NTA2, 350NTTA2, NT-855, NTA-855, NTTA-855-G2. Check it applies to your exact model before use.
Applies to: Cummins/Onan 350NTTA2, Cummins/Onan NT-855-G2 engine, Cummins/Onan NT-855-G4 engine, Cummins/Onan NT-855-G3 engine, Cummins/Onan NT-855-G6 engine, Cummins/Onan NTA-855-G1 engine, Cummins/Onan NTA-855-G2 engine, Cummins/Onan NTTA-855-G2 engine
Before you start
- Allow cooling system to cool before releasing pressure and removing radiator cap.
Procedure
- Disconnect coolant heater from AC power; remove radiator/expansion tank cap.
- Open draincock, disconnect lower radiator hose or remove heat exchanger drain plug.
- Remove pipe plug from water pump body; open cylinder block and oil cooler draincocks; drain completely.
- Close block and oil cooler draincocks; replace water pump pipe plug.
- Close draincock and reconnect hose or replace drain plug.
- Fill with clean water, leave cap off, operate engine 5 minutes above 194 F (90 C).
- Shut off engine and drain; repeat until flush water is clean.
- Drain completely, then fill cooling system with proper coolant.
Specs & values
- Flush at above 194 F (90 C) for 5 minutes
Full service-parts list: Cummins/Onan 350NTTA2 →
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.