Cummins/Onan — Draining and Refilling the Cooling System
Maintenance · Engine cooling system
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan HDKA, Cummins/Onan HDKAJ, Cummins/Onan HDKAK
Before you start
- Hot coolant spray can cause severe burns. Let the engine cool before releasing the pressure cap or removing the drain cap.
- Ethylene glycol antifreeze is toxic; dispose of it according to local regulations.
Procedure
- Allow engine to cool; turn pressure cap slowly to relieve pressure, then remove.
- Drain coolant by removing the system drain cap into a suitable container.
- Fill recovery tank with coolant mixture to the COLD mark.
- Secure drain cap; fill system through pressure cap/fill opening.
- Pull hose connected to pressure cap assembly out as far as it will go.
- Start and operate genset a few minutes under load; shut it down.
- Add more coolant if necessary and secure the pressure cap.
- Check coolant level in recovery tank before first startup of each day.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Use 50/50 ethylene glycol/water mixture
- Cooling system capacity 4.2 quart (4 l)
- Pressure cap 14 psi
Full service-parts list: Cummins/Onan HDKA →, Cummins/Onan HDKAJ →, Cummins/Onan HDKAK →
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.