Cummins/Onan — Filling Hydraulic System With Oil
Maintenance
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Rotating drive shafts can cause severe personal injury or death. Guards must be provided.
- High pressure spray from a leak can penetrate skin. Wear safety glasses. Shut down engine before loosening fittings.
- Running the pump without oil will quickly destroy the pump.
Procedure
- Complete all hydraulic and electric connections and secure any shaft guards.
- Turn the genset switch OFF and make sure all loads are disconnected by turning the line circuit breaker OFF.
- Connect a 1000 psi gauge (with snubber) to system pressure port M2 or charge pressure gauge port M3.
- Remove the fitting at the top pump case drain (Port L1 or L2), fill the pump with oil and reconnect.
- Fill the oil reservoir to within 1/4 inch of the top of the sight glass. Wait 1/2 hour for air to escape and refill.
- If possible, disable engine starting and crank the engine to fill the system with oil. Otherwise, start and run the engine for not more than 3 to 5 seconds at a time.
- Refill the reservoir if the level drops.
- Repeat Steps 6 and 7 until the system is full. Stop the engine when the pressure gauge indicates at least 200 psi.
- With the engine stopped, remove the pressure gauge and install the port plug.
- When the system is full, turn the genset switch ON, let the engine run and listen for pump noise. Stop the engine or disengage the PTO clutch immediately if the pump is noisy. Repeat Steps 6 and 7.
Tools required
- 1000 psi gauge with snubber Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Fill oil reservoir to within 1/4 inch of top of sight glass
- Pressure gauge should indicate at least 200 psi when full
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.