Cummins/Onan — Draining and Cleaning the Cooling System
Maintenance · Engine Cooling System
From a Cummins/Onan operator's manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MDKB, Cummins/Onan MDKBH
Before you start
- Hot coolant spray can cause severe burns. Let the engine cool before releasing the pressure cap or removing the drain cap.
Procedure
- Have towels and containers ready to collect and dispose of the coolant.
- Disconnect the negative (-) battery cable, let the engine cool and remove the front and top access doors and the coolant pressure cap.
- Drain the exhaust manifold/coolant reservoir by disconnecting the hose at the coolant pump inlet and twisting it down into a container.
- Drain the block by removing the cap on the drain fitting on the left side of the block using an 11/16 inch socket, swivel and 12 to 18 inch extension.
- Use radiator cleaning chemicals to clean and flush the system, following the cleaner manufacturer's instructions.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Full service-parts list: Cummins/Onan MDKB →, Cummins/Onan MDKBH →
Source: Cummins/Onan operator'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.