Cummins/Onan — Cooling system drain and flush
Maintenance · Cooling system / heat exchanger
From a Cummins/Onan owner's manual covering: CFP15E, CFP23E, CFP30E, CFP50, CFP5E, CFP60E, CFP7E, CFP9E, CFP9E HHP. Check it applies to your exact model before use.
Applies to: Cummins/Onan CFP23E
Before you start
- Do not remove pressure cap from hot engine; wait until below 50 C (120 F).
- Coolant is toxic - dispose per regulations.
Procedure
- Disconnect both batteries (negative first).
- Remove coolant expansion tank pressure/fill cap.
- Disconnect engine coolant heater power supply.
- Place container (min 57 L) under coolant drain valve.
- Open the drain petcock and drain coolant; drain engine heater.
- Flush with clean fresh water or heat exchanger cleaner.
- Install new coolant filter if needed.
- Fill with 50/50 antifreeze mixture and vent air.
- Operate engine to 82 C (180 F) and check for leaks.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Fill mixture 50% water / 50% ethylene-glycol protects to -37 C (-34 F)
Full service-parts list: Cummins/Onan CFP23E →
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.