Cummins/Onan 20W-20 — Flushing Cooling System
Maintenance
For the Cummins/Onan 20W-20, from the Cummins/Onan service manual.
Applies to: Cummins/Onan 20W-20, Cummins/Onan RDJF engine
Procedure
- Drain radiator, cylinder block and exhaust manifold.
- Remove inlet and outlet hoses between engine and radiator.
- Close all drain plugs; attach flushing gun nozzle to water outlet.
- Restrict inlet opening until system fills with water, then apply air pressure gradually.
- Repeat until water from cylinder block flows clean.
- Remove flushing gun.
- Reinstall thermostats, hoses and drain plugs; refill with proper coolant.
- Check system for leaks.
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 20W-20 →
Source: Cummins/Onan service 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.