Low lube oil pressure after a generator service
A 300 kW diesel generator on a local vessel has just had its lube oil and filters changed. After restart, oil pressure reads 1.9 bar at 1,500 rpm, against a normal 3.2-3.6 bar, oil temperature is 95°C, and the engine emits blue smoke. The oil pressure gauge is mechanical; the new filter is a non-genuine element; the oil level is at the dipstick full mark. The vessel is due to sail in 40 minutes with 60 passengers. The engineer has a spare genuine filter and 20 L of SAE 15W-40 oil; the manual specifies SAE 15W-40 API CF-4 and a 12 L sump. A junior engineer added 4 L of SAE 40 oil from an unlabelled drum before the run. The generator is the only source of electrical power for the passenger launch.
1. List the checks you would make before accepting the low pressure reading, and explain what each check could reveal.
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Checks and what they reveal
- Verify the gauge. Fit a known-good mechanical gauge at the test point. A faulty gauge is common after work near the engine and would explain a false low reading.
- Check the filter element and part number. A non-genuine filter may have the wrong relief valve, a collapsed element or a missing O-ring. That can bypass oil straight back to the sump and drop pressure. Compare it with the genuine spare.
- Check oil level and condition. Overfilling causes aeration and foaming, which lowers pressure and can produce blue smoke. The 4 L of unlabelled SAE 40 may also be the wrong grade or contaminated. Drain a sample, smell for fuel dilution and check viscosity.
- Check the suction and relief valve. A leaking suction joint or a relief valve stuck open will reduce pressure. Look for oil weeping at the filter head and pump unions.
- Check for blue smoke cause. Blue smoke can be lube oil burning through the exhaust, or fuel dilution causing poor combustion. Overfill and wrong oil grade are the first suspects here.
Reasoning Do not assume the engine is worn out. The pressure was normal before the service, so the work just done is the most likely cause. The generator is the only electrical source, so a wrong diagnosis either way is a safety issue.
2. The genuine filter is fitted, excess oil is drained to the correct level, and the pressure is still 2.0 bar after ten minutes. The vessel is due to sail. What is your decision, and how do you communicate it?
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Decision: do not sail on this generator until the cause is found.
A sustained 2.0 bar against a normal 3.2-3.6 bar is not a minor gauge error. If the bearings are being starved, the generator can seize, black out the vessel and leave 60 passengers without lighting, radio or bilge pumps. The fact that the vessel is due to sail in 40 minutes is commercial pressure, not a technical argument.
Communication Tell the master plainly: the generator is not fit for the passenger run, the pressure is below limit after correct oil and filter, and the next step is to inspect the suction, relief valve and bearings or arrange shore power. Advise the company to delay the sailing or provide a substitute vessel. Record the readings, the filter change, the oil grade added and the decision in the engine room log.
If a short onward passage is unavoidable It should only be to a nearby safe berth, with the master's agreement, reduced electrical load and continuous monitoring. Even then, be ready to stop. Do not carry passengers on a trip of any length with an unreliable sole source of electrical power.