Cummins/Onan — Flush cooling system
Maintenance
From a Cummins/Onan service manual covering: 10MJC, 15MJC, 3MJA, 4MJA, 5MJB, 705MJB. Check it applies to your exact model before use.
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Procedure
- Remove thermostat and water pump cover.
- Restrict pump opening partially.
- Attach flushing gun nozzle to thermostat opening.
- Fill block with water, apply air pressure.
- Repeat until water runs clean.
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.