Cummins/Onan — Coolant Change and Flushing the System
Maintenance · cooling system
From a Cummins/Onan owner's manual covering: 6C8.3, 6CT 8.3, 6CTA8.3. Check it applies to your exact model before use.
Applies to: Cummins/Onan 6CTA8.3, Cummins/Onan C Series, Cummins/Onan 6CT8.3 engine
Before you start
- Wait until temperature is below 50C [120F] before removing the coolant system pressure cap
- Do not install the radiator cap during flushing
Procedure
- Wait until temperature is below 50C [120F] before removing pressure cap.
- Open drain valve on radiator and oil cooler; drain the system.
- Check for damaged hoses and loose clamps; replace as required.
- Fill with sodium carbonate and water mixture; open vent petcocks.
- Operate engine 5 minutes above 80C [180F]; shut off and drain.
- Fill with clean water; operate 5 minutes; drain again.
- Fill with 50 percent water and 50 percent ethylene-glycol antifreeze.
- Install pressure cap; operate to 80C [180F] and check for leaks.
Tools required
- Drain pan capacity 20 litres [5 U.S. gallons] Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Use 0.5 kilogram [1.0 pound] sodium carbonate per 23 litres [6.0 U.S. gallons] water
- Vent fill rate 38 litres/minute [10 U.S. gallon/minute]
Full service-parts list: Cummins/Onan C Series →
Source: Cummins/Onan owner's 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.