Cummins/Onan — Flushing the Cooling System
Maintenance
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Procedure
- Drain the radiator, cylinder block and exhaust manifold.
- Remove the inlet and outlet hoses between the engine and radiator.
- Close all drain plugs and attach the flushing gun nozzle to the water outlet, near the exhaust manifold.
- Restrict the inlet line opening until the system fills with water, then apply air pressure gradually.
- Repeat until water from the cylinder block flows clean.
- Remove the flushing gun.
- Reinstall thermostats, hoses and drain plugs and refill with proper coolant.
- Check the system thoroughly for leaks.
Tools required
- Flushing gun Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
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.