Cummins/Onan — Cooling system cleaning and flushing
Maintenance
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Never pour cold water into a hot engine; doing so may crack head or cylinder block.
- Cleaning solutions can cause burns; read warning labels.
Procedure
- Drain system and fill with clean water and approved chemical cleaner.
- Follow cleaner supplier instructions for cleaning.
- When cleaning is complete, drain cleaning solution and flush system.
- Reverse flush engine and radiator or heat exchanger for best results.
- Allow engine to cool as much as possible before flushing with cold water.
- If optional water jacket tank heater is used, drain and flush it also.
Tools required
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.