Cummins/Onan — Flushing and Cleaning the Cooling System
Maintenance · coolant system
From a Cummins/Onan operator's manual covering: KTA51, KTA52, KTA53, KTA54, KTT52. Check it applies to your exact model before use.
Applies to: Cummins/Onan DFLA, Cummins/Onan DFLB, Cummins/Onan DFLC, Cummins/Onan DFM, Cummins/Onan KTT52
Before you start
- Excessive air pressure while starting the water flow could split the radiator core. Apply air pressure gradually to avoid damage.
Procedure
- Use a good cooling system cleaner such as sodium bisulphate or oxalic acid and follow the supplier's instructions.
- Neutralize and flush with clean water.
- Open the upper and lower radiator hose connections and install the radiator cap.
- Attach a flushing gun nozzle to the lower radiator hose connection and let water run until the radiator is full.
- Gradually apply air pressure to avoid damaging the core; shut off air and allow radiator to refill.
- Repeat flushing procedure until water coming from the radiator is clean.
- To flush the engine block, remove the thermostat, attach the flushing gun to the upper radiator hose and fill the block with water.
- Restrict the lower radiator hose opening until the block is filled, apply air pressure and force water from the lower opening.
- Repeat until water from the lower radiator hose is clean.
- Replace the thermostat and all hoses and refill cooling system.
Tools required
- Flushing gun nozzle Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Full service-parts list: Cummins/Onan DFLB →, Cummins/Onan DFLC →, Cummins/Onan KTT52 →
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.