Cummins/Onan — Cooling System Flushing (RCCK)
Maintenance
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MCCK
Before you start
- Do not open a radiator pressure cap when coolant temperature is above 212 F (100 C) or while engine is running.
Procedure
- Remove both thermostats.
- Attach a flushing gun nozzle to the thermostat opening and fill the block with water.
- Apply air pressure.
- Repeat the process until water coming from the block is clean.
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 MCCK →
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.